add auto-merge workflow for all PRs

.github/workflows/auto-merge.yml

@@ -0,0 +1,21 @@
+name: auto-merge
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    branches: [main]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  enable-auto-merge:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Enable auto-merge
+        run: gh pr merge --auto --squash "$PR_NUMBER"
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_REPO: ${{ github.repository }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}