purge old images. keep 5 more recent

.github/workflows/build-debian-images.yaml

@@ -47,3 +47,29 @@ jobs:
         if: ${{ github.event_name != 'pull_request' }}
         run: |
           docker push ${{ env.image-id-lowercase }}:${{ env.IMAGE_TAG }}
+
+  purge-old-images:
+    name: Purge old images.
+    # if: ${{ github.event.schedule || github.event.workflow_dispatch }}
+    # Delete below
+    if: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' || github.event_name == 'push' }}
+    strategy:
+      matrix:
+        include:
+        - image-id: debian-11-pdns-base
+        - image-id: debian-12-pdns-base
+    runs-on: ubuntu-22.04
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Get repository name
+        run: |
+          echo "repo-name=${{ github.repository }}" | cut -d '/' -f 2  >> "$GITHUB_ENV"
+
+      - name: Purge old images keeping the 5 more recent ones
+        uses: actions/delete-package-versions@v4
+        with: 
+          package-name: ${{ env.repo-name }}/${{ matrix.debian-release-name }}
+          package-type: container
+          min-versions-to-keep: 5