ci(workflows): cleanup PR Docker images

.github/workflows/__delete.yml

@@ -0,0 +1,24 @@
+on:
+  workflow_call:
+    inputs:
+      gotenberg_version:
+        type: string
+        required: true
+      alternate_repository:
+        type: string
+        default: ''
+
+permissions:
+  contents: read
+
+jobs:
+  delete:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Delete
+        uses: gotenberg/gotenberg-release-action/actions/delete@main
+        with:
+          docker_hub_username: ${{ secrets.DOCKERHUB_USERNAME }}
+          docker_hub_password: ${{ secrets.DOCKERHUB_TOKEN }}
+          version: ${{ inputs.gotenberg_version }}
+          alternate_repository: ${{ inputs.alternate_repository }}

.github/workflows/pull-request-cleanup.yml

@@ -0,0 +1,18 @@
+name: Pull Request Cleanup
+
+on:
+  pull_request:
+    types: [ closed ]
+
+permissions:
+  contents: read
+
+jobs:
+
+  cleanup:
+    name: Cleanup
+    uses: ./.github/workflows/__delete.yml
+    secrets: inherit
+    with:
+      gotenberg_version: pr-${{ github.event.pull_request.number }}
+      alternate_repository: snapshot