Plugin Extensions: Notify on core Grafana changes (#108005)

* feat: introduce a Github workflow that is notifying on extension related changes

* review: fix review notes

* review: remove broken heart

* fix: use a new version of the send-slack-message action

.github/CODEOWNERS

@@ -801,6 +801,7 @@ embed.go @grafana/grafana-as-code
 /.github/workflows/commands.yml @torkelo
 /.github/workflows/community-release.yml @grafana/grafana-developer-enablement-squad
 /.github/workflows/detect-breaking-changes-* @grafana/plugins-platform-frontend
+/.github/workflows/detect-plugin-extension-changes.yml @grafana/plugins-platform-frontend
 /.github/workflows/documentation-ci.yml @grafana/docs-tooling
 /.github/workflows/deploy-pr-preview.yml @grafana/docs-tooling
 /.github/workflows/feature-toggles-ci.yml @grafana/docs-tooling