added proper templating section

Author: g0rgamesh

example_grafana_dashboard.json

@@ -858,7 +858,22 @@
   "style": "dark",
   "tags": [],
   "templating": {
-    "list": []
+    "list": [
+      {
+        "current": {
+          "text": "Prometheus",
+          "value": "Prometheus"
+        },
+        "hide": 0,
+        "label": null,
+        "name": "DS_PROMETHEUS",
+        "options": [],
+        "query": "prometheus",
+        "refresh": 1,
+        "regex": "",
+        "type": "datasource"
+      }
+    ]
   },
   "time": {
     "from": "now-1h",