Add automerge workflow

Author: peter-evans

.github/workflows/automerge-dependabot.yml

@@ -0,0 +1,16 @@
+name: Auto-merge Dependabot
+on: pull_request
+
+permissions:
+  pull-requests: write
+
+jobs:
+  automerge:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - uses: peter-evans/enable-pull-request-automerge@v2
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          pull-request-number: ${{ github.event.pull_request.number }}
+          merge-method: squash