docs: Add detailed docstrings to API models and update OpenAPI spec (#2889)

This PR focuses on improving the developer experience by adding
comprehensive docstrings to the API data models across the Llama Stack.
These docstrings provide detailed explanations for each model and its
fields, making the API easier to understand and use.

**Key changes:**
- **Added Docstrings:** Added reST formatted docstrings to Pydantic
models in the `llama_stack/apis/` directory. This includes models for:
  - Agents (`agents.py`)
  - Benchmarks (`benchmarks.py`)
  - Datasets (`datasets.py`)
  - Inference (`inference.py`)
  - And many other API modules.
- **OpenAPI Spec Update:** Regenerated the OpenAPI specification
(`docs/_static/llama-stack-spec.yaml` and
`docs/_static/llama-stack-spec.html`) to include the new docstrings.
This will be reflected in the API documentation, providing richer
information to users.

**Impact:**
- Developers using the Llama Stack API will have a better understanding
of the data structures.
- The auto-generated API documentation is now more informative.

---------

Co-authored-by: Ashwin Bharambe <ashwin.bharambe@gmail.com>

llama_stack/apis/datasets/datasets.py

@@ -94,6 +94,10 @@ register_schema(DataSource, name="DataSource")
 class CommonDatasetFields(BaseModel):
     """
     Common fields for a dataset.
+
+    :param purpose: Purpose of the dataset indicating its intended use
+    :param source: Data source configuration for the dataset
+    :param metadata: Additional metadata for the dataset
     """
 
     purpose: DatasetPurpose
@@ -106,6 +110,11 @@ class CommonDatasetFields(BaseModel):
 
 @json_schema_type
 class Dataset(CommonDatasetFields, Resource):
+    """Dataset resource for storing and accessing training or evaluation data.
+
+    :param type: Type of resource, always 'dataset' for datasets
+    """
+
     type: Literal[ResourceType.dataset] = ResourceType.dataset
 
     @property
@@ -118,10 +127,20 @@ class Dataset(CommonDatasetFields, Resource):
 
 
 class DatasetInput(CommonDatasetFields, BaseModel):
+    """Input parameters for dataset operations.
+
+    :param dataset_id: Unique identifier for the dataset
+    """
+
     dataset_id: str
 
 
 class ListDatasetsResponse(BaseModel):
+    """Response from listing datasets.
+
+    :param data: List of datasets
+    """
+
     data: list[Dataset]