fix(experiments): create a shared retention metric (#42462)

Author: rodrigoi

ee/clickhouse/views/experiment_saved_metrics.py

@@ -12,6 +12,7 @@
     ExperimentMeanMetric,
     ExperimentMetricType,
     ExperimentRatioMetric,
+    ExperimentRetentionMetric,
     ExperimentTrendsQuery,
 )
 
@@ -88,8 +89,12 @@ def validate_query(self, value):
                     ExperimentFunnelMetric(**metric_query)
                 elif metric_query["metric_type"] == ExperimentMetricType.RATIO:
                     ExperimentRatioMetric(**metric_query)
+                elif metric_query["metric_type"] == ExperimentMetricType.RETENTION:
+                    ExperimentRetentionMetric(**metric_query)
                 else:
-                    raise ValidationError("ExperimentMetric metric_type must be 'mean', 'funnel', or 'ratio'")
+                    raise ValidationError(
+                        "ExperimentMetric metric_type must be 'mean', 'funnel', 'ratio', or 'retention'"
+                    )
             elif metric_query["kind"] == "ExperimentTrendsQuery":
                 ExperimentTrendsQuery(**metric_query)
             elif metric_query["kind"] == "ExperimentFunnelsQuery":

ee/clickhouse/views/test/test_experiment_saved_metrics.py

@@ -259,7 +259,9 @@ def test_create_saved_metric_with_experiment_metric_invalid_metric_type(self):
         )
 
         self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
-        self.assertIn("ExperimentMetric metric_type must be 'mean', 'funnel', or 'ratio'", response.json()["detail"])
+        self.assertIn(
+            "ExperimentMetric metric_type must be 'mean', 'funnel', 'ratio', or 'retention'", response.json()["detail"]
+        )
 
     def test_create_saved_metric_with_experiment_metric_ratio(self):
         response = self.client.post(