configure automerge of dependency update PRs

Author: tjenkinson

.github/workflows/automerge.yml

@@ -0,0 +1,14 @@
+name: Auto Merge Dependency Updates
+
+on:
+  - pull_request
+  - pull_request_review
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: tjenkinson/gh-action-auto-merge-dependency-updates@af6d2a7
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          allowed-actors: dependabot[bot]