change schema -> dataset_schema for register_dataset api (#443)

# What does this PR do?

- API updates: change schema to dataset_schema for register_dataset for
resolving pydantic naming conflict
- Note: this OpenAPI update will be synced with
llama-stack-client-python SDK.

cc @dineshyv 

## Test Plan

```
pytest -v -s -m meta_reference_eval_together_inference_huggingface_datasetio eval/test_eval.py
```

## Sources

Please link relevant resources if necessary.


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [ ] Ran pre-commit to handle lint / formatting issues.
- [ ] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/apis/datasets/datasets.py

@@ -49,7 +49,7 @@ class Datasets(Protocol):
     async def register_dataset(
         self,
         dataset_id: str,
-        schema: Dict[str, ParamType],
+        dataset_schema: Dict[str, ParamType],
         url: URL,
         provider_dataset_id: Optional[str] = None,
         provider_id: Optional[str] = None,