github-action: undeploy serverless for closed PRs using ci:project-deploy-observability (#182374)

Automate the undeployment for all those Kibana PRs using the label
`ci:project-deploy-observability` once those PRs have been closed
(merged, closed).

This will help with tidying up all the ongoing deployments that were
created automatically as part of the recent automation with
https://github.com/elastic/kibana/pull/181851

.github/CODEOWNERS

@@ -1030,6 +1030,7 @@ packages/kbn-monaco/src/esql @elastic/kibana-esql
 
 # Observability robots
 /.github/workflows/deploy-my-kibana.yml @elastic/observablt-robots
+/.github/workflows/undeploy-my-kibana.yml @elastic/observablt-robots
 /.github/workflows/oblt-github-commands @elastic/observablt-robots
 
 # Infra Monitoring

.github/workflows/undeploy-my-kibana.yml

@@ -0,0 +1,32 @@
+---
+##
+## This the automation will undeploy an existing automated deployment
+## caused by a merged/closed event and if the GitHub label matches
+## the automated one.
+##
+## Owner: @elastic/observablt-robots
+## Further details: https://ela.st/oblt-deploy-my-kibana
+##
+name: undeploy-my-kibana
+
+on:
+  pull_request:
+    types: [closed]
+
+permissions:
+  contents: read
+
+jobs:
+  undeploy-my-kibana:
+    if: contains(github.event.pull_request.labels.*.name, 'ci:project-deploy-observability')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: elastic/apm-pipeline-library/.github/actions/github-token@current
+        with:
+          url: ${{ secrets.OBLT_VAULT_ADDR }}
+          roleId: ${{ secrets.OBLT_VAULT_ROLE_ID }}
+          secretId: ${{ secrets.OBLT_VAULT_SECRET_ID }}
+
+      - uses: elastic/apm-pipeline-library/.github/actions/undeploy-my-kibana@current
+        with:
+          token: ${{ env.GITHUB_TOKEN }}