feat: introduce /admin API for stack administration and operations (#4401)

# What does this PR do?

- Add new /admin API (v1alpha) for administrative operations including
provider management, health checks, version info, and route listing
- Implement using FastAPI routers following batches pattern with proper
request/response models
- Endpoints: /admin/providers, /admin/providers/{id},
/admin/inspect/routes, /admin/health, /admin/version
- Create admin module structure: models.py, api.py, fastapi_routes.py,
init.py
- Add AdminImpl in llama_stack/core combining provider and inspect
functionality
- Deprecate standalone /providers and /inspect APIs (remain functional
for backward compatibility)
- Consolidate duplicate types: ProviderInfo, HealthInfo, RouteInfo, etc.
now defined once in admin.models

## Test Plan

new admin integration suite, uses generated stainless SDK, and records
new tests on this PR.

Signed-off-by: Charlie Doern <cdoern@redhat.com>

src/llama_stack_api/providers/models.py

@@ -6,38 +6,19 @@
 
 """Pydantic models for Providers API requests and responses.
 
-This module defines the request and response models for the Providers API
-using Pydantic with Field descriptions for OpenAPI schema generation.
+This module re-exports models from llama_stack_api.admin.models to ensure
+a single source of truth and avoid type conflicts.
 """
 
-from typing import Any
+# Import and re-export shared models from admin
+from llama_stack_api.admin.models import (
+    InspectProviderRequest,
+    ListProvidersResponse,
+    ProviderInfo,
+)
 
-from pydantic import BaseModel, Field
-
-from llama_stack_api.datatypes import HealthResponse
-from llama_stack_api.schema_utils import json_schema_type
-
-
-@json_schema_type
-class ProviderInfo(BaseModel):
-    """Information about a registered provider including its configuration and health status."""
-
-    api: str = Field(..., description="The API name this provider implements")
-    provider_id: str = Field(..., description="Unique identifier for the provider")
-    provider_type: str = Field(..., description="The type of provider implementation")
-    config: dict[str, Any] = Field(..., description="Configuration parameters for the provider")
-    health: HealthResponse = Field(..., description="Current health status of the provider")
-
-
-@json_schema_type
-class ListProvidersResponse(BaseModel):
-    """Response containing a list of all available providers."""
-
-    data: list[ProviderInfo] = Field(..., description="List of provider information objects")
-
-
-@json_schema_type
-class InspectProviderRequest(BaseModel):
-    """Request model for inspecting a provider by ID."""
-
-    provider_id: str = Field(..., description="The ID of the provider to inspect.")
+__all__ = [
+    "ProviderInfo",
+    "ListProvidersResponse",
+    "InspectProviderRequest",
+]