CI: Add GitHub workflow to schedule a PR with changes to Alerting Swagger spec (#71794)

* add github workflow to schedule alerting swagger spec pr

* also generate stable api spec

.github/CODEOWNERS

@@ -594,6 +594,7 @@ embed.go @grafana/grafana-as-code
 /.github/pr-commands.json @marefr
 /.github/renovate.json5 @grafana/frontend-ops
 /.github/teams.yml @armandgrillet
+/.github/workflows/alerting-swagger-gen.yml @grafana/alerting-backend-product
 /.github/workflows/auto-milestone.yml @grafana/grafana-delivery
 /.github/workflows/backport.yml @grafana/grafana-delivery
 /.github/workflows/bump-version.yml @grafana/grafana-delivery