prom: enable min interval per panel

This commit makes it possible to set min interval per panel.
Overrides the value configured on the datasource.

ref #9705

public/app/plugins/datasource/prometheus/plugin.json

@@ -13,6 +13,10 @@
   "alerting": true,
   "annotations": true,
 
+  "queryOptions": {
+    "minInterval": true
+  },
+
   "info": {
     "author": {
       "name": "Grafana Project",