github: enable mirroring to gitlab

.github/workflows/mirror.yml

@@ -0,0 +1,25 @@
+name: Mirror and run GitLab CI
+
+on:
+  push:
+
+jobs:
+  to_gitlab:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    - name: Mirror + trigger CI
+      uses: SvanBoxel/[email protected]
+      with:
+        args: "https://gitlab.desy.de/dcache/www-dcache-org"
+      env:
+        FOLLOW_TAGS: "true"
+        FORCE_PUSH: "false"
+        GITLAB_HOSTNAME: "gitlab.desy.de"
+        GITLAB_USERNAME: "dcache"
+        GITLAB_PASSWORD: ${{ secrets.GITLAB_PASSWORD }}
+        GITLAB_PROJECT_ID: "15155"
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        POLL_TIMEOUT: 60