feat: add optional metrics under API /providers

- add field "metrcis" under API "/providers"
- each provider can config "metrics" in run.yaml in "config"
  - if no "metrics":  /provider/<provider_id> shows "metrics: null" in response
  - if has "metrics": /provider/<provider_id> show result in response
  - if has "metrics" but is not string type and not httpurl, raise ValidationError
- add unit tests for providers
- update "docs"

Signed-off-by: Wen Zhou <wenzhou@redhat.com>

tests/unit/distribution/test_providers.py

@@ -0,0 +1,113 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+
+import pytest
+
+from llama_stack.apis.providers import ProviderInfo
+from llama_stack.distribution.datatypes import Provider, StackRunConfig
+from llama_stack.distribution.providers import ProviderImpl, ProviderImplConfig
+
+
+class TestProviderImpl:
+    """Test suite for ProviderImpl class."""
+
+    @pytest.fixture
+    def mock_config(self):
+        """Create a mock configuration for testing."""
+        run_config = StackRunConfig(
+            image_name="test_image",
+            providers={
+                "inference": [
+                    Provider(
+                        provider_id="test_provider_with_metrics_url",
+                        provider_type="test_type1",
+                        config={"url": "http://localhost:8000", "metrics": "http://localhost:9090/metrics"},
+                    ),
+                    Provider(
+                        provider_id="test_provider_no_metrics_url",
+                        provider_type="test_type2",
+                        config={"url": "http://localhost:8080"},
+                    ),
+                ]
+            },
+        )
+        return ProviderImplConfig(run_config=run_config)
+
+    @pytest.fixture
+    def mock_deps(self):
+        """Create mock dependencies."""
+        return {}
+
+    @pytest.mark.asyncio
+    async def test_provider_info_structure(self, mock_config, mock_deps):
+        """Test ProviderInfo objects"""
+        provider_impl = ProviderImpl(mock_config, mock_deps)
+
+        response = await provider_impl.list_providers()
+        provider = response.data[0]
+
+        # Check all required fields
+        assert hasattr(provider, "api")
+        assert isinstance(provider.api, str)
+
+        assert hasattr(provider, "provider_id")
+        assert isinstance(provider.provider_id, str)
+
+        assert hasattr(provider, "provider_type")
+        assert isinstance(provider.provider_type, str)
+
+        assert hasattr(provider, "config")
+        assert isinstance(provider.config, dict)
+
+        assert hasattr(provider, "health")
+
+        assert provider.metrics is None or isinstance(provider.metrics, str)
+
+    @pytest.mark.asyncio
+    async def test_list_providers_with_metrics(self, mock_config, mock_deps):
+        """Test list_providers includes metrics field."""
+        provider_impl = ProviderImpl(mock_config, mock_deps)
+
+        response = await provider_impl.list_providers()
+
+        assert response is not None
+        assert len(response.data) == 2
+
+        # Check provider with metrics
+        provider1 = response.data[0]
+        assert isinstance(provider1, ProviderInfo)
+        assert provider1.provider_id == "test_provider_with_metrics_url"
+        assert provider1.metrics == "http://localhost:9090/metrics"
+
+        # Check provider without metrics
+        provider2 = response.data[1]
+        assert isinstance(provider2, ProviderInfo)
+        assert provider2.provider_id == "test_provider_no_metrics_url"
+        assert provider2.metrics is None
+
+    @pytest.mark.asyncio
+    async def test_inspect_provider_with_metrics(self, mock_config, mock_deps):
+        """Test inspect_provider includes metrics field."""
+        provider_impl = ProviderImpl(mock_config, mock_deps)
+
+        # Test provider with metrics
+        provider_info = await provider_impl.inspect_provider("test_provider_with_metrics_url")
+        assert provider_info.provider_id == "test_provider_with_metrics_url"
+        assert provider_info.metrics == "http://localhost:9090/metrics"
+
+        # Test provider without metrics
+        provider_info = await provider_impl.inspect_provider("test_provider_no_metrics_url")
+        assert provider_info.provider_id == "test_provider_no_metrics_url"
+        assert provider_info.metrics is None
+
+    @pytest.mark.asyncio
+    async def test_inspect_provider_not_found(self, mock_config, mock_deps):
+        """Test inspect_provider raises error for non-existent provider."""
+        provider_impl = ProviderImpl(mock_config, mock_deps)
+
+        with pytest.raises(ValueError, match="Provider nonexistent not found"):
+            await provider_impl.inspect_provider("nonexistent")