Alerting: Handle image renderer unavailable when edit notifiers (#23711)

If no image renderer available/installed when adding a new  alert notification 
channel will set Include image to false per default, otherwise true as before.
If no image renderer available/installed when adding/edit alert notification 
channel will show an informational message that you need to install the 
Grafana Image Renderer plugin for Grafana to be able to render an image. 

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

public/app/features/alerting/NotificationsEditCtrl.ts

@@ -4,6 +4,7 @@ import { getBackendSrv } from '@grafana/runtime';
 import { AppEvents } from '@grafana/data';
 import { IScope } from 'angular';
 import { promiseToDigest } from '../../core/utils/promiseToDigest';
+import config from 'app/core/config';
 
 export class AlertNotificationEditCtrl {
   theForm: any;
@@ -27,6 +28,7 @@ export class AlertNotificationEditCtrl {
     isDefault: false,
   };
   getFrequencySuggestion: any;
+  rendererAvailable: boolean;
 
   /** @ngInject */
   constructor(
@@ -43,6 +45,9 @@ export class AlertNotificationEditCtrl {
       return ['1m', '5m', '10m', '15m', '30m', '1h'];
     };
 
+    this.defaults.settings.uploadImage = config.rendererAvailable;
+    this.rendererAvailable = config.rendererAvailable;
+
     promiseToDigest(this.$scope)(
       getBackendSrv()
         .get(`/api/alert-notifiers`)

public/app/features/alerting/partials/notification_edit.html

@@ -32,6 +32,16 @@
           checked="ctrl.model.settings.uploadImage"
           tooltip="Captures an image and include it in the notification">
       </gf-form-switch>
+      <div class="grafana-info-box m-t-2" ng-show="ctrl.model.settings.uploadImage && !ctrl.rendererAvailable">
+        <h5>No image renderer available/installed</h5>
+        <p>
+          Grafana cannot find an image renderer to capture an image for the notification.
+          Please make sure the <a href="https://grafana.com/grafana/plugins/grafana-image-renderer" target="_blank" rel="noreferrer">Grafana Image Renderer plugin</a> is installed.
+        </p>
+        <p>
+          Please contact your Grafana administrator to install the plugin.
+        </p>
+      </div>
       <gf-form-switch
           class="gf-form"
           label="Disable Resolve Message"