Configure Prometheus alerts for Elasticsearch

2 kinds of alers:
- cluster health status
- disk allocation watermark (per node)

Change-Id: I0d168ba899d8a168543c8ba0a63793001e46267b
diff --git a/metadata/service/support.yml b/metadata/service/support.yml
index 3f37b10..4e2c98a 100644
--- a/metadata/service/support.yml
+++ b/metadata/service/support.yml
@@ -13,3 +13,5 @@
         enabled: true
       grafana:
         enabled: true
+      prometheus:
+        enabled: true