Chore: Notify in slack when nightly docker image scan fails (#34980)

* Add scan docker image step, when pipeline fails notify in slack channel

* Add star code that generates the yaml file for the fail message to slack

* Fix template message

* Make message more detailed

* Adjust the name of the step

.drone.yml

@@ -3457,6 +3457,17 @@ steps:
   - trivy --exit-code 1 --severity HIGH,CRITICAL grafana/grafana:latest-ubuntu
   - trivy --exit-code 1 --severity HIGH,CRITICAL grafana/grafana:main-ubuntu
 
+- name: slack-notify-failure
+  image: plugins/slack
+  settings:
+    channel: grafana-backend
+    template: "Nightly docker image scan job for {{repo.name}} failed: {{build.link}}"
+    webhook:
+      from_secret: slack_webhook
+  when:
+    status:
+    - failure
+
 trigger:
   cron:
   - nightly