feat: Add OpenAI Conversations API (#3429)

# What does this PR do?

Initial implementation for `Conversations` and `ConversationItems` using
`AuthorizedSqlStore` with endpoints to:
- CREATE
- UPDATE
- GET/RETRIEVE/LIST
- DELETE

Set `level=LLAMA_STACK_API_V1`.

NOTE: This does not currently incorporate changes for Responses, that'll
be done in a subsequent PR.

Closes https://github.com/llamastack/llama-stack/issues/3235

## Test Plan
- Unit tests
- Integration tests

Also comparison of [OpenAPI spec for OpenAI
API](https://github.com/openai/openai-openapi/tree/manual_spec)
```bash
oasdiff breaking --fail-on ERR docs/static/llama-stack-spec.yaml https://raw.githubusercontent.com/openai/openai-openapi/refs/heads/manual_spec/openapi.yaml --strip-prefix-base "/v1/openai/v1" \
--match-path '(^/v1/openai/v1/conversations.*|^/conversations.*)'
```

Note I still have some uncertainty about this, I borrowed this info from
@cdoern on https://github.com/llamastack/llama-stack/pull/3514 but need
to spend more time to confirm it's working, at the moment it suggests it
does.

UPDATE on `oasdiff`, I investigated the OpenAI spec further and it looks
like currently the spec does not list Conversations, so that analysis is
useless. Noting for future reference.

---------

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

tests/integration/conversations/test_openai_conversations.py

@@ -0,0 +1,135 @@
+# 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
+
+
+@pytest.mark.integration
+class TestOpenAIConversations:
+    # TODO: Update to compat_client after client-SDK is generated
+    def test_conversation_create(self, openai_client):
+        conversation = openai_client.conversations.create(
+            metadata={"topic": "demo"}, items=[{"type": "message", "role": "user", "content": "Hello!"}]
+        )
+
+        assert conversation.id.startswith("conv_")
+        assert conversation.object == "conversation"
+        assert conversation.metadata["topic"] == "demo"
+        assert isinstance(conversation.created_at, int)
+
+    def test_conversation_retrieve(self, openai_client):
+        conversation = openai_client.conversations.create(metadata={"topic": "demo"})
+
+        retrieved = openai_client.conversations.retrieve(conversation.id)
+
+        assert retrieved.id == conversation.id
+        assert retrieved.object == "conversation"
+        assert retrieved.metadata["topic"] == "demo"
+        assert retrieved.created_at == conversation.created_at
+
+    def test_conversation_update(self, openai_client):
+        conversation = openai_client.conversations.create(metadata={"topic": "demo"})
+
+        updated = openai_client.conversations.update(conversation.id, metadata={"topic": "project-x"})
+
+        assert updated.id == conversation.id
+        assert updated.metadata["topic"] == "project-x"
+        assert updated.created_at == conversation.created_at
+
+    def test_conversation_delete(self, openai_client):
+        conversation = openai_client.conversations.create(metadata={"topic": "demo"})
+
+        deleted = openai_client.conversations.delete(conversation.id)
+
+        assert deleted.id == conversation.id
+        assert deleted.object == "conversation.deleted"
+        assert deleted.deleted is True
+
+    def test_conversation_items_create(self, openai_client):
+        conversation = openai_client.conversations.create()
+
+        items = openai_client.conversations.items.create(
+            conversation.id,
+            items=[
+                {"type": "message", "role": "user", "content": [{"type": "input_text", "text": "Hello!"}]},
+                {"type": "message", "role": "user", "content": [{"type": "input_text", "text": "How are you?"}]},
+            ],
+        )
+
+        assert items.object == "list"
+        assert len(items.data) == 2
+        assert items.data[0].content[0].text == "Hello!"
+        assert items.data[1].content[0].text == "How are you?"
+        assert items.first_id == items.data[0].id
+        assert items.last_id == items.data[1].id
+        assert items.has_more is False
+
+    def test_conversation_items_list(self, openai_client):
+        conversation = openai_client.conversations.create()
+
+        openai_client.conversations.items.create(
+            conversation.id,
+            items=[{"type": "message", "role": "user", "content": [{"type": "input_text", "text": "Hello!"}]}],
+        )
+
+        items = openai_client.conversations.items.list(conversation.id, limit=10)
+
+        assert items.object == "list"
+        assert len(items.data) >= 1
+        assert items.data[0].type == "message"
+        assert items.data[0].role == "user"
+        assert hasattr(items, "first_id")
+        assert hasattr(items, "last_id")
+        assert hasattr(items, "has_more")
+
+    def test_conversation_item_retrieve(self, openai_client):
+        conversation = openai_client.conversations.create()
+
+        created_items = openai_client.conversations.items.create(
+            conversation.id,
+            items=[{"type": "message", "role": "user", "content": [{"type": "input_text", "text": "Hello!"}]}],
+        )
+
+        item_id = created_items.data[0].id
+        item = openai_client.conversations.items.retrieve(item_id, conversation_id=conversation.id)
+
+        assert item.id == item_id
+        assert item.type == "message"
+        assert item.role == "user"
+        assert item.content[0].text == "Hello!"
+
+    def test_conversation_item_delete(self, openai_client):
+        conversation = openai_client.conversations.create()
+
+        created_items = openai_client.conversations.items.create(
+            conversation.id,
+            items=[{"type": "message", "role": "user", "content": [{"type": "input_text", "text": "Hello!"}]}],
+        )
+
+        item_id = created_items.data[0].id
+        deleted = openai_client.conversations.items.delete(item_id, conversation_id=conversation.id)
+
+        assert deleted.id == item_id
+        assert deleted.object == "conversation.item.deleted"
+        assert deleted.deleted is True
+
+    def test_full_workflow(self, openai_client):
+        conversation = openai_client.conversations.create(
+            metadata={"topic": "workflow-test"}, items=[{"type": "message", "role": "user", "content": "Hello!"}]
+        )
+
+        openai_client.conversations.items.create(
+            conversation.id,
+            items=[{"type": "message", "role": "user", "content": [{"type": "input_text", "text": "Follow up"}]}],
+        )
+
+        all_items = openai_client.conversations.items.list(conversation.id)
+        assert len(all_items.data) >= 2
+
+        updated = openai_client.conversations.update(conversation.id, metadata={"topic": "workflow-complete"})
+        assert updated.metadata["topic"] == "workflow-complete"
+
+        openai_client.conversations.delete(conversation.id)