Add Grafana Oncall notification provider (#2783)

* Add Grafana Oncall notification provider

* Fix linter errors

* Remove useless variables

* Remove test message

Co-authored-by: Frank Elsinga <frank@elsinga.de>

* spelling consistency

* Update server/notification-providers/grafana-oncall.js

Co-authored-by: Frank Elsinga <frank@elsinga.de>

* Update server/notification-providers/grafana-oncall.js

Co-authored-by: Frank Elsinga <frank@elsinga.de>

* eslint requirements

Co-authored-by: Matthew Nickson <mnickson@sidingsmedia.com>

* Add Grafana Oncall translation

* Update src/components/notifications/GrafanaOncall.vue

Co-authored-by: Frank Elsinga <frank@elsinga.de>

* Check empty url

---------

Co-authored-by: Emmanuel Cohen <emmanuel.cohen@bso.co>
Co-authored-by: Frank Elsinga <frank@elsinga.de>
Co-authored-by: Matthew Nickson <mnickson@sidingsmedia.com>
Co-authored-by: Louis Lam <louislam@users.noreply.github.com>

src/components/NotificationDialog.vue

@@ -119,6 +119,7 @@ export default {
                 "GoogleChat": "Google Chat (Google Workspace)",
                 "gorush": "Gorush",
                 "gotify": "Gotify",
+                "GrafanaOncall": "Grafana Oncall",
                 "HomeAssistant": "Home Assistant",
                 "Kook": "Kook",
                 "line": "LINE Messenger",