added elasticsearch health check rule

templates/prometheus/config/prometheus/alert.rules.j2

@@ -340,3 +340,13 @@ groups:
     annotations:
       summary: "Too many request against digitalocean API. plz check."
       description: "Alert for request against digitalocean API."
+
+  - alert: elasticsearch health status not green
+    expr: avg(elasticsearch_cluster_health_status{color="green"}) < 1
+    for: 2m
+    labels:
+      severity: critical
+    annotations:
+      summary: "Elasticsearch health status is not green. Please Check"
+      description: "Alert for Elasticsearch health status"
+