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>

llama_stack/core/stack.py

@@ -24,6 +24,7 @@ from llama_stack.apis.inference import Inference
 from llama_stack.apis.inspect import Inspect
 from llama_stack.apis.models import Models
 from llama_stack.apis.post_training import PostTraining
+from llama_stack.apis.prompts import Prompts
 from llama_stack.apis.providers import Providers
 from llama_stack.apis.safety import Safety
 from llama_stack.apis.scoring import Scoring
@@ -37,6 +38,7 @@ from llama_stack.apis.vector_io import VectorIO
 from llama_stack.core.datatypes import Provider, StackRunConfig
 from llama_stack.core.distribution import get_provider_registry
 from llama_stack.core.inspect import DistributionInspectConfig, DistributionInspectImpl
+from llama_stack.core.prompts.prompts import PromptServiceConfig, PromptServiceImpl
 from llama_stack.core.providers import ProviderImpl, ProviderImplConfig
 from llama_stack.core.resolver import ProviderRegistry, resolve_impls
 from llama_stack.core.routing_tables.common import CommonRoutingTableImpl
@@ -72,6 +74,7 @@ class LlamaStack(
     ToolRuntime,
     RAGToolRuntime,
     Files,
+    Prompts,
 ):
     pass
 
@@ -305,6 +308,12 @@ def add_internal_implementations(impls: dict[Api, Any], run_config: StackRunConf
     )
     impls[Api.providers] = providers_impl
 
+    prompts_impl = PromptServiceImpl(
+        PromptServiceConfig(run_config=run_config),
+        deps=impls,
+    )
+    impls[Api.prompts] = prompts_impl
+
 
 # Produces a stack of providers for the given run config. Not all APIs may be
 # asked for in the run config.
@@ -329,6 +338,9 @@ async def construct_stack(
     # Add internal implementations after all other providers are resolved
     add_internal_implementations(impls, run_config)
 
+    if Api.prompts in impls:
+        await impls[Api.prompts].initialize()
+
     await register_resources(run_config, impls)
 
     await refresh_registry_once(impls)