feat: Add OpenAI compat /v1/vector_store APIs (#2423)

Adding OpenAI compat `/v1/vector-store` apis. 
This PR implements the `faiss` provider with followup PRs coming up for
other providers.

Added routes to create, update, delete, list vector stores. 
Also added route to search a vector store

Inserting into vector stores is missing and will be a follow up diff. 

### Test Plan 
- Added new integration test for testing the faiss provider 
```
pytest -sv --stack-config http://localhost:8321 tests/integration/vector_io/test_openai_vector_stores.py --embedding-model all-MiniLM-L6-v2
```

llama_stack/apis/vector_io/vector_io.py

@@ -37,6 +37,85 @@ class QueryChunksResponse(BaseModel):
     scores: list[float]
 
 
+@json_schema_type
+class VectorStoreObject(BaseModel):
+    """OpenAI Vector Store object."""
+
+    id: str
+    object: str = "vector_store"
+    created_at: int
+    name: str | None = None
+    usage_bytes: int = 0
+    file_counts: dict[str, int] = Field(default_factory=dict)
+    status: str = "completed"
+    expires_after: dict[str, Any] | None = None
+    expires_at: int | None = None
+    last_active_at: int | None = None
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+@json_schema_type
+class VectorStoreCreateRequest(BaseModel):
+    """Request to create a vector store."""
+
+    name: str | None = None
+    file_ids: list[str] = Field(default_factory=list)
+    expires_after: dict[str, Any] | None = None
+    chunking_strategy: dict[str, Any] | None = None
+    metadata: dict[str, Any] = Field(default_factory=dict)
+
+
+@json_schema_type
+class VectorStoreModifyRequest(BaseModel):
+    """Request to modify a vector store."""
+
+    name: str | None = None
+    expires_after: dict[str, Any] | None = None
+    metadata: dict[str, Any] | None = None
+
+
+@json_schema_type
+class VectorStoreListResponse(BaseModel):
+    """Response from listing vector stores."""
+
+    object: str = "list"
+    data: list[VectorStoreObject]
+    first_id: str | None = None
+    last_id: str | None = None
+    has_more: bool = False
+
+
+@json_schema_type
+class VectorStoreSearchRequest(BaseModel):
+    """Request to search a vector store."""
+
+    query: str | list[str]
+    filters: dict[str, Any] | None = None
+    max_num_results: int = 10
+    ranking_options: dict[str, Any] | None = None
+    rewrite_query: bool = False
+
+
+@json_schema_type
+class VectorStoreSearchResponse(BaseModel):
+    """Response from searching a vector store."""
+
+    object: str = "vector_store.search_results.page"
+    search_query: str
+    data: list[dict[str, Any]]
+    has_more: bool = False
+    next_page: str | None = None
+
+
+@json_schema_type
+class VectorStoreDeleteResponse(BaseModel):
+    """Response from deleting a vector store."""
+
+    id: str
+    object: str = "vector_store.deleted"
+    deleted: bool = True
+
+
 class VectorDBStore(Protocol):
     def get_vector_db(self, vector_db_id: str) -> VectorDB | None: ...
 
@@ -81,3 +160,116 @@ class VectorIO(Protocol):
         :returns: A QueryChunksResponse.
         """
         ...
+
+    # OpenAI Vector Stores API endpoints
+    @webmethod(route="/openai/v1/vector_stores", method="POST")
+    async def openai_create_vector_store(
+        self,
+        name: str | None = None,
+        file_ids: list[str] | None = None,
+        expires_after: dict[str, Any] | None = None,
+        chunking_strategy: dict[str, Any] | None = None,
+        metadata: dict[str, Any] | None = None,
+        embedding_model: str | None = None,
+        embedding_dimension: int | None = 384,
+        provider_id: str | None = None,
+        provider_vector_db_id: str | None = None,
+    ) -> VectorStoreObject:
+        """Creates a vector store.
+
+        :param name: A name for the vector store.
+        :param file_ids: A list of File IDs that the vector store should use. Useful for tools like `file_search` that can access files.
+        :param expires_after: The expiration policy for a vector store.
+        :param chunking_strategy: The chunking strategy used to chunk the file(s). If not set, will use the `auto` strategy.
+        :param metadata: Set of 16 key-value pairs that can be attached to an object.
+        :param embedding_model: The embedding model to use for this vector store.
+        :param embedding_dimension: The dimension of the embedding vectors (default: 384).
+        :param provider_id: The ID of the provider to use for this vector store.
+        :param provider_vector_db_id: The provider-specific vector database ID.
+        :returns: A VectorStoreObject representing the created vector store.
+        """
+        ...
+
+    @webmethod(route="/openai/v1/vector_stores", method="GET")
+    async def openai_list_vector_stores(
+        self,
+        limit: int = 20,
+        order: str = "desc",
+        after: str | None = None,
+        before: str | None = None,
+    ) -> VectorStoreListResponse:
+        """Returns a list of vector stores.
+
+        :param limit: A limit on the number of objects to be returned. Limit can range between 1 and 100, and the default is 20.
+        :param order: Sort order by the `created_at` timestamp of the objects. `asc` for ascending order and `desc` for descending order.
+        :param after: A cursor for use in pagination. `after` is an object ID that defines your place in the list.
+        :param before: A cursor for use in pagination. `before` is an object ID that defines your place in the list.
+        :returns: A VectorStoreListResponse containing the list of vector stores.
+        """
+        ...
+
+    @webmethod(route="/openai/v1/vector_stores/{vector_store_id}", method="GET")
+    async def openai_retrieve_vector_store(
+        self,
+        vector_store_id: str,
+    ) -> VectorStoreObject:
+        """Retrieves a vector store.
+
+        :param vector_store_id: The ID of the vector store to retrieve.
+        :returns: A VectorStoreObject representing the vector store.
+        """
+        ...
+
+    @webmethod(route="/openai/v1/vector_stores/{vector_store_id}", method="POST")
+    async def openai_update_vector_store(
+        self,
+        vector_store_id: str,
+        name: str | None = None,
+        expires_after: dict[str, Any] | None = None,
+        metadata: dict[str, Any] | None = None,
+    ) -> VectorStoreObject:
+        """Updates a vector store.
+
+        :param vector_store_id: The ID of the vector store to update.
+        :param name: The name of the vector store.
+        :param expires_after: The expiration policy for a vector store.
+        :param metadata: Set of 16 key-value pairs that can be attached to an object.
+        :returns: A VectorStoreObject representing the updated vector store.
+        """
+        ...
+
+    @webmethod(route="/openai/v1/vector_stores/{vector_store_id}", method="DELETE")
+    async def openai_delete_vector_store(
+        self,
+        vector_store_id: str,
+    ) -> VectorStoreDeleteResponse:
+        """Delete a vector store.
+
+        :param vector_store_id: The ID of the vector store to delete.
+        :returns: A VectorStoreDeleteResponse indicating the deletion status.
+        """
+        ...
+
+    @webmethod(route="/openai/v1/vector_stores/{vector_store_id}/search", method="POST")
+    async def openai_search_vector_store(
+        self,
+        vector_store_id: str,
+        query: str | list[str],
+        filters: dict[str, Any] | None = None,
+        max_num_results: int = 10,
+        ranking_options: dict[str, Any] | None = None,
+        rewrite_query: bool = False,
+    ) -> VectorStoreSearchResponse:
+        """Search for chunks in a vector store.
+
+        Searches a vector store for relevant chunks based on a query and optional file attribute filters.
+
+        :param vector_store_id: The ID of the vector store to search.
+        :param query: The query string or array for performing the search.
+        :param filters: Filters based on file attributes to narrow the search results.
+        :param max_num_results: Maximum number of results to return (1 to 50 inclusive, default 10).
+        :param ranking_options: Ranking options for fine-tuning the search results.
+        :param rewrite_query: Whether to rewrite the natural language query for vector search (default false)
+        :returns: A VectorStoreSearchResponse containing the search results.
+        """
+        ...