ci: Setup auto rebase (#3431)

.github/workflows/rebase.yml

@@ -0,0 +1,20 @@
+name: Rebase Pull Request
+on:
+  issue_comment:
+    types: [created]
+
+jobs:
+  rebase:
+    name: Rebase
+    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/rebase') && github.event.comment.author_association == 'MEMBER'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v2.4.0
+        with:
+          token: ${{ secrets.REBASE_TOKEN }}
+          fetch-depth: 0
+      - name: Automatic Rebase
+        uses: cirrus-actions/rebase@1.5
+        env:
+          GITHUB_TOKEN: ${{ secrets.REBASE_TOKEN }}