feat: Added an Fast API new endpoint to serve eval metric info

This endpoint could be used by ADK Web to dynamically know:
- What are the available eval metrics in an App
- A description of those metrics
- A value range supported by those metrics

We also update the metric registry to make it mandatory to supply these details. The goal is to improve usability and interpretability of the eval metrics.

PiperOrigin-RevId: 787277695

tests/unittests/evaluation/test_response_evaluator.py

@@ -16,6 +16,7 @@
 from unittest.mock import patch
 
 from google.adk.evaluation.eval_case import Invocation
+from google.adk.evaluation.eval_metrics import PrebuiltMetrics
 from google.adk.evaluation.evaluator import EvalStatus
 from google.adk.evaluation.response_evaluator import ResponseEvaluator
 from google.genai import types as genai_types
@@ -113,3 +114,29 @@ class TestResponseEvaluator:
     assert [m.name for m in mock_kwargs["metrics"]] == [
         vertexai_types.PrebuiltMetric.COHERENCE.name
     ]
+
+  def test_get_metric_info_response_evaluation_score(self, mock_perform_eval):
+    """Test get_metric_info function for response evaluation metric."""
+    metric_info = ResponseEvaluator.get_metric_info(
+        PrebuiltMetrics.RESPONSE_EVALUATION_SCORE.value
+    )
+    assert (
+        metric_info.metric_name
+        == PrebuiltMetrics.RESPONSE_EVALUATION_SCORE.value
+    )
+    assert metric_info.metric_value_info.interval.min_value == 1.0
+    assert metric_info.metric_value_info.interval.max_value == 5.0
+
+  def test_get_metric_info_response_match_score(self, mock_perform_eval):
+    """Test get_metric_info function for response match metric."""
+    metric_info = ResponseEvaluator.get_metric_info(
+        PrebuiltMetrics.RESPONSE_MATCH_SCORE.value
+    )
+    assert metric_info.metric_name == PrebuiltMetrics.RESPONSE_MATCH_SCORE.value
+    assert metric_info.metric_value_info.interval.min_value == 0.0
+    assert metric_info.metric_value_info.interval.max_value == 1.0
+
+  def test_get_metric_info_invalid(self, mock_perform_eval):
+    """Test get_metric_info function for invalid metric."""
+    with pytest.raises(ValueError):
+      ResponseEvaluator.get_metric_info("invalid_metric")