Added auto-lock to github mirror

.github/workflows/lockdown.yml

@@ -0,0 +1,34 @@
+name: 'Lock down repository'
+
+on:
+  issues:
+    types: opened
+  pull_request:
+    types: opened
+
+jobs:
+  lockdown:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/repo-lockdown@v2
+        with:
+          github-token: ${{ github.token }}
+          issue-labels: 'off-topic'
+          issue-comment: >
+            Thanks for your contribution!
+            
+            However, this repository does not accept bug reports,
+            since this is only a mirror of
+            https://gitlab.com/1O/bitwarden_rs-backup.
+
+            Please feel free to open the issue there.
+          skip-closed-issue-comment: true
+          pr-comment: >
+            Thanks for your contribution!
+          
+            However, this repository does not accept pull requests,
+            since this is only a mirror of
+            https://gitlab.com/1O/bitwarden_rs-backup.
+
+            Please feel free to open the pull request there.
+          skip-closed-pr-comment: true