add sandbox deletion (#5674)

.github/workflows/sandbox-deletion.yaml

@@ -0,0 +1,25 @@
+name: Remove sandbox environment
+
+on:
+  pull_request:
+    types: [closed]
+
+jobs:
+  delete:
+    if: startsWith(github.event.pull_request.head.ref, 'sandbox/')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ secrets.APP_ID }}
+          private-key: ${{ secrets.PRIVATE_KEY }}
+          owner: ${{ github.repository_owner }}
+
+      - name: Repository dispatch
+        uses: peter-evans/repository-dispatch@v2
+        with:
+          token: ${{ steps.app-token.outputs.token }}
+          repository: kubeshop/testkube-deployment
+          event-type: sandbox_env_delete
+          client-payload: '{"ref_name": "${{ github.event.pull_request.head.ref }}"}'