AMBARI-15021. Set AMBARI_METRICS as the default datasource. (Prajwal Rao via yusaku)

ambari-server/src/main/resources/common-services/AMBARI_METRICS/0.1.0/package/templates/metrics_grafana_datasource.json.j2

@@ -28,6 +28,6 @@
   "basicAuthUser": "",
   "basicAuthPassword": "",
   "withCredentials": false,
-  "isDefault": false,
+  "isDefault": true,
   "jsonData": {}
-}
+}