feat: Adding OpenAI Prompts API (#3319)

# What does this PR do?
This PR adds support for OpenAI Prompts API.

Note, OpenAI does not explicitly expose the Prompts API but instead
makes it available in the Responses API and in the [Prompts
Dashboard](https://platform.openai.com/docs/guides/prompting#create-a-prompt).

I have added the following APIs:
- CREATE
- GET
- LIST
- UPDATE
- Set Default Version

The Set Default Version API is made available only in the Prompts
Dashboard and configures which prompt version is returned in the GET
(the latest version is the default).

Overall, the expected functionality in Responses will look like this:

```python
from openai import OpenAI
client = OpenAI()

response = client.responses.create(
  prompt={
    "id": "pmpt_68b0c29740048196bd3a6e6ac3c4d0e20ed9a13f0d15bf5e",
    "version": "2",
    "variables": {
        "city": "San Francisco",
        "age": 30,
    }
  }
)
```

### Resolves https://github.com/llamastack/llama-stack/issues/3276


## Test Plan
Unit tests added. Integration tests can be added after client
generation.

## Next Steps
1. Update Responses API to support Prompt API
2. I'll enhance the UI to implement the Prompt Dashboard. 
3. Add cache for lower latency

---------

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

tests/unit/prompts/prompts/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.

tests/unit/prompts/prompts/conftest.py

@@ -0,0 +1,30 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+import random
+
+import pytest
+
+from llama_stack.core.prompts.prompts import PromptServiceConfig, PromptServiceImpl
+from llama_stack.providers.utils.kvstore.config import SqliteKVStoreConfig
+
+
+@pytest.fixture
+async def temp_prompt_store(tmp_path_factory):
+    unique_id = f"prompt_store_{random.randint(1, 1000000)}"
+    temp_dir = tmp_path_factory.getbasetemp()
+    db_path = str(temp_dir / f"{unique_id}.db")
+
+    from llama_stack.core.datatypes import StackRunConfig
+    from llama_stack.providers.utils.kvstore import kvstore_impl
+
+    mock_run_config = StackRunConfig(image_name="test-distribution", apis=[], providers={})
+    config = PromptServiceConfig(run_config=mock_run_config)
+    store = PromptServiceImpl(config, deps={})
+
+    store.kvstore = await kvstore_impl(SqliteKVStoreConfig(db_path=db_path))
+
+    yield store

tests/unit/prompts/prompts/test_prompts.py

@@ -0,0 +1,144 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+
+import pytest
+
+
+class TestPrompts:
+    async def test_create_and_get_prompt(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("Hello world!", ["name"])
+        assert prompt.prompt == "Hello world!"
+        assert prompt.version == 1
+        assert prompt.prompt_id.startswith("pmpt_")
+        assert prompt.variables == ["name"]
+
+        retrieved = await temp_prompt_store.get_prompt(prompt.prompt_id)
+        assert retrieved.prompt_id == prompt.prompt_id
+        assert retrieved.prompt == prompt.prompt
+
+    async def test_update_prompt(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("Original")
+        updated = await temp_prompt_store.update_prompt(prompt.prompt_id, "Updated", 1, ["v"])
+        assert updated.version == 2
+        assert updated.prompt == "Updated"
+
+    async def test_update_prompt_with_version(self, temp_prompt_store):
+        version_for_update = 1
+
+        prompt = await temp_prompt_store.create_prompt("Original")
+        assert prompt.version == 1
+        prompt = await temp_prompt_store.update_prompt(prompt.prompt_id, "Updated", version_for_update, ["v"])
+        assert prompt.version == 2
+
+        with pytest.raises(ValueError):
+            # now this is a stale version
+            await temp_prompt_store.update_prompt(prompt.prompt_id, "Another Update", version_for_update, ["v"])
+
+        with pytest.raises(ValueError):
+            # this version does not exist
+            await temp_prompt_store.update_prompt(prompt.prompt_id, "Another Update", 99, ["v"])
+
+    async def test_delete_prompt(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("to be deleted")
+        await temp_prompt_store.delete_prompt(prompt.prompt_id)
+        with pytest.raises(ValueError):
+            await temp_prompt_store.get_prompt(prompt.prompt_id)
+
+    async def test_list_prompts(self, temp_prompt_store):
+        response = await temp_prompt_store.list_prompts()
+        assert response.data == []
+
+        await temp_prompt_store.create_prompt("first")
+        await temp_prompt_store.create_prompt("second")
+
+        response = await temp_prompt_store.list_prompts()
+        assert len(response.data) == 2
+
+    async def test_version(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("V1")
+        await temp_prompt_store.update_prompt(prompt.prompt_id, "V2", 1)
+
+        v1 = await temp_prompt_store.get_prompt(prompt.prompt_id, version=1)
+        assert v1.version == 1 and v1.prompt == "V1"
+
+        latest = await temp_prompt_store.get_prompt(prompt.prompt_id)
+        assert latest.version == 2 and latest.prompt == "V2"
+
+    async def test_set_default_version(self, temp_prompt_store):
+        prompt0 = await temp_prompt_store.create_prompt("V1")
+        prompt1 = await temp_prompt_store.update_prompt(prompt0.prompt_id, "V2", 1)
+
+        assert (await temp_prompt_store.get_prompt(prompt0.prompt_id)).version == 2
+        prompt_default = await temp_prompt_store.set_default_version(prompt0.prompt_id, 1)
+        assert (await temp_prompt_store.get_prompt(prompt0.prompt_id)).version == 1
+        assert prompt_default.version == 1
+
+        prompt2 = await temp_prompt_store.update_prompt(prompt0.prompt_id, "V3", prompt1.version)
+        assert prompt2.version == 3
+
+    async def test_prompt_id_generation_and_validation(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("Test")
+        assert prompt.prompt_id.startswith("pmpt_")
+        assert len(prompt.prompt_id) == 53
+
+        with pytest.raises(ValueError):
+            await temp_prompt_store.get_prompt("invalid_id")
+
+    async def test_list_shows_default_versions(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("V1")
+        await temp_prompt_store.update_prompt(prompt.prompt_id, "V2", 1)
+        await temp_prompt_store.update_prompt(prompt.prompt_id, "V3", 2)
+
+        response = await temp_prompt_store.list_prompts()
+        listed_prompt = response.data[0]
+        assert listed_prompt.version == 3 and listed_prompt.prompt == "V3"
+
+        await temp_prompt_store.set_default_version(prompt.prompt_id, 1)
+
+        response = await temp_prompt_store.list_prompts()
+        listed_prompt = response.data[0]
+        assert listed_prompt.version == 1 and listed_prompt.prompt == "V1"
+        assert not (await temp_prompt_store.get_prompt(prompt.prompt_id, 3)).is_default
+
+    async def test_get_all_prompt_versions(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("V1")
+        await temp_prompt_store.update_prompt(prompt.prompt_id, "V2", 1)
+        await temp_prompt_store.update_prompt(prompt.prompt_id, "V3", 2)
+
+        versions = (await temp_prompt_store.list_prompt_versions(prompt.prompt_id)).data
+        assert len(versions) == 3
+        assert [v.version for v in versions] == [1, 2, 3]
+        assert [v.is_default for v in versions] == [False, False, True]
+
+        await temp_prompt_store.set_default_version(prompt.prompt_id, 2)
+        versions = (await temp_prompt_store.list_prompt_versions(prompt.prompt_id)).data
+        assert [v.is_default for v in versions] == [False, True, False]
+
+        with pytest.raises(ValueError):
+            await temp_prompt_store.list_prompt_versions("nonexistent")
+
+    async def test_prompt_variable_validation(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("Hello {{ name }}, you live in {{ city }}!", ["name", "city"])
+        assert prompt.variables == ["name", "city"]
+
+        prompt_no_vars = await temp_prompt_store.create_prompt("Hello world!", [])
+        assert prompt_no_vars.variables == []
+
+        with pytest.raises(ValueError, match="undeclared variables"):
+            await temp_prompt_store.create_prompt("Hello {{ name }}, invalid {{ unknown }}!", ["name"])
+
+    async def test_update_prompt_set_as_default_behavior(self, temp_prompt_store):
+        prompt = await temp_prompt_store.create_prompt("V1")
+        assert (await temp_prompt_store.get_prompt(prompt.prompt_id)).version == 1
+
+        prompt_v2 = await temp_prompt_store.update_prompt(prompt.prompt_id, "V2", 1, [], set_as_default=True)
+        assert prompt_v2.version == 2
+        assert (await temp_prompt_store.get_prompt(prompt.prompt_id)).version == 2
+
+        prompt_v3 = await temp_prompt_store.update_prompt(prompt.prompt_id, "V3", 2, [], set_as_default=False)
+        assert prompt_v3.version == 3
+        assert (await temp_prompt_store.get_prompt(prompt.prompt_id)).version == 2