[docs] add openapi spec to docs (#508)

# What does this PR do?
- modify openapi generator to add coming soon tag for unimplemented api
- sphinx-redocs extension for openapi spec to readthedocs page

## Test Plan



https://github.com/user-attachments/assets/b4c7eebc-2361-4198-a987-dbfbcff914cf






## 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.

docs/openapi_generator/pyopenapi/generator.py

@@ -438,6 +438,14 @@ class Generator:
         return extra_tags
 
     def _build_operation(self, op: EndpointOperation) -> Operation:
+        if op.defining_class.__name__ in [
+            "SyntheticDataGeneration",
+            "PostTraining",
+            "BatchInference",
+        ]:
+            op.defining_class.__name__ = f"{op.defining_class.__name__} (Coming Soon)"
+            print(op.defining_class.__name__)
+
         doc_string = parse_type(op.func_ref)
         doc_params = dict(
             (param.name, param.description) for param in doc_string.params.values()