azuremonitor: simple alerting for Azure Monitor API

Lots of edge cases and functionality left to implement but
a simple query works for alerting now.

public/app/plugins/datasource/grafana-azure-monitor-datasource/plugin.json

@@ -158,5 +158,6 @@
   },
 
   "metrics": true,
-  "annotations": true
+  "annotations": true,
+  "alerting": true
 }