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/providers/providers.py

@@ -14,6 +14,15 @@ from llama_stack.schema_utils import json_schema_type, webmethod
 
 @json_schema_type
 class ProviderInfo(BaseModel):
+    """Information about a registered provider including its configuration and health status.
+
+    :param api: The API name this provider implements
+    :param provider_id: Unique identifier for the provider
+    :param provider_type: The type of provider implementation
+    :param config: Configuration parameters for the provider
+    :param health: Current health status of the provider
+    """
+
     api: str
     provider_id: str
     provider_type: str
@@ -22,6 +31,11 @@ class ProviderInfo(BaseModel):
 
 
 class ListProvidersResponse(BaseModel):
+    """Response containing a list of all available providers.
+
+    :param data: List of provider information objects
+    """
+
     data: list[ProviderInfo]