fix: add missing files provider to NVIDIA distribution (#3479)

# What does this PR do?
The rag-runtime tool requires files API as a dependency, but the NVIDIA
distribution was missing the files provider configuration. Thus, when
running:

```
llama stack build --distro nvidia --image-type venv
```
And then:
```
llama stack run {path_to_distribution_config} --image-type venv
```
It would raise an error:
```
RuntimeError: Failed to resolve 'tool_runtime' provider 'rag-runtime' of type 'inline::rag-runtime': required dependency 'files' is not available. Please add a 'files' provider to your configuration or check if the provider is properly configured.
```

This PR fixes the issue by adding missing files provider to NVIDIA
distribution.

## Test Plan
N/A

llama_stack/distributions/nvidia/run.yaml

@@ -4,6 +4,7 @@ apis:
 - agents
 - datasetio
 - eval
+- files
 - inference
 - post_training
 - safety
@@ -77,6 +78,14 @@ providers:
   tool_runtime:
   - provider_id: rag-runtime
     provider_type: inline::rag-runtime
+  files:
+  - provider_id: meta-reference-files
+    provider_type: inline::localfs
+    config:
+      storage_dir: ${env.FILES_STORAGE_DIR:=~/.llama/distributions/nvidia/files}
+      metadata_store:
+        type: sqlite
+        db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/nvidia}/files_metadata.db
 metadata_store:
   type: sqlite
   db_path: ${env.SQLITE_STORE_DIR:=~/.llama/distributions/nvidia}/registry.db