update config example: add elasticsearch config example

Author: wuriyanto48

config_example.json

@@ -42,6 +42,13 @@
             "enable": true
         },
 
+        "elasticsearch_cluster_one": {
+            "kind": "web",
+            "url": "http://elastic:devpass@localhost:9200/_cluster/health?pretty",
+            "checkInterval": 10,
+            "enable": true
+        },
+
         "dummy_one": {
             "kind": "dummy",
             "url": "https://minio-storage.com/minio/health/ready",