feat: Add S3 Files Provider implementation

Implements a complete S3-based file storage provider for Llama Stack with:

Core Implementation:
- S3FilesImpl class with full OpenAI Files API compatibility
- Support for file upload, download, listing, deletion operations
- Sqlite-based metadata storage for fast queries and API compliance
- Configurable S3 endpoints (AWS, MinIO, LocalStack support)

Key Features:
- Automatic S3 bucket creation and management
- Metadata persistence
- Proper error handling for S3 connectivity and permissions

Dependencies:
- Adds boto3 for AWS S3 integration
- Adds moto[s3] for testing infrastructure

Testing:

 Unit: `./scripts/unit-tests.sh tests/unit/files tests/unit/providers/files`

 Integration:

  Start MinIO: `podman run --rm -it -p 9000:9000 minio/minio server /data`

  Start stack w/ S3 provider: `S3_ENDPOINT_URL=http://localhost:9000 AWS_ACCESS_KEY_ID=minioadmin AWS_SECRET_ACCESS_KEY=minioadmin S3_BUCKET_NAME=llama-stack-files uv run llama stack build --image-type venv --providers files=remote::s3 --run`

  Run integration tests: `./scripts/integration-tests.sh --stack-config http://localhost:8321 --provider ollama --test-subdirs files`

scripts/provider_codegen.py

@@ -157,12 +157,14 @@ def get_config_class_info(config_class_path: str) -> dict[str, Any]:
         }
 
 
-def generate_provider_docs(provider_spec: Any, api_name: str) -> str:
+def generate_provider_docs(progress, provider_spec: Any, api_name: str) -> str:
     """Generate markdown documentation for a provider."""
     provider_type = provider_spec.provider_type
     config_class = provider_spec.config_class
 
     config_info = get_config_class_info(config_class)
+    if "error" in config_info:
+        progress.print(config_info["error"])
 
     md_lines = []
     md_lines.append(f"# {provider_type}")
@@ -295,7 +297,7 @@ def process_provider_registry(progress, change_tracker: ChangedPathTracker) -> N
                 filename = provider_type.replace("::", "_").replace(":", "_")
                 provider_doc_file = doc_output_dir / f"{filename}.md"
 
-                provider_docs = generate_provider_docs(provider, api_name)
+                provider_docs = generate_provider_docs(progress, provider, api_name)
 
                 provider_doc_file.write_text(provider_docs)
                 change_tracker.add_paths(provider_doc_file)