chore: OpenAI compatibility for Milvus (#2470)

# What does this PR do?
Closes https://github.com/meta-llama/llama-stack/issues/2461



## Test Plan
Tested with the `ollama` distriubtion template and updated the vector_io
provider to:
```yaml
vector_io:
- provider_id: milvus
  provider_type: inline::milvus
  config:
    db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/ollama}/milvus_store.db
    kvstore:
      type: sqlite
      db_name: milvus_registry.db
```

Ran the stack
```bash
llama stack run ./llama_stack/templates/ollama/run.yaml --image-type venv --env OLLAMA_URL="http://0.0.0.0:11434"
```

Ran the tests:
```
pytest -sv --stack-config=http://localhost:8321 tests/integration/vector_io/test_openai_vector_stores.py  --embedding-model all-MiniLM-L6-v2
```
Output passed.

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

llama_stack/providers/registry/vector_io.py

@@ -130,5 +130,6 @@ def available_providers() -> list[ProviderSpec]:
             module="llama_stack.providers.inline.vector_io.milvus",
             config_class="llama_stack.providers.inline.vector_io.milvus.MilvusVectorIOConfig",
             api_dependencies=[Api.inference],
+            optional_api_dependencies=[Api.files],
         ),
     ]