Implement attaching files to vector stores

This adds the ability to attach files to vector
stores (client.vector_stores.files.create) for the OpenAI Vector
Stores Files API.

The initial implementation is only for Faiss, and tested via the
existing test_responses.py::test_response_non_streaming_file_search.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

llama_stack/providers/registry/vector_io.py

@@ -31,7 +31,7 @@ def available_providers() -> list[ProviderSpec]:
             pip_packages=["faiss-cpu"],
             module="llama_stack.providers.inline.vector_io.faiss",
             config_class="llama_stack.providers.inline.vector_io.faiss.FaissVectorIOConfig",
-            api_dependencies=[Api.inference],
+            api_dependencies=[Api.inference, Api.files],
         ),
         # NOTE: sqlite-vec cannot be bundled into the container image because it does not have a
         # source distribution and the wheels are not available for all platforms.