Add reusable Dependabot automerge workflow

.github/dependabot.yml

@@ -8,3 +8,7 @@ updates:
       - "Dependencies"
     cooldown:
       default-days: 1
+    groups:
+      github-actions:
+        patterns:
+          - "*"

.github/workflows/dependabot_automerge.yml

@@ -0,0 +1,21 @@
+jobs:
+  automerge:
+    name: Dependabot automerge
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    permissions:
+      contents: write # required to merge the pull request
+      pull-requests: write # required to enable auto-merge on the pull request
+    runs-on: ubuntu-latest
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@25dd0e34f4fe68f24cc83900b1fe3fe149efef98 # v3.1.0
+      - name: Enable auto-merge
+        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          PR_URL: ${{ github.event.pull_request.html_url }}
+        run: gh pr merge --auto --merge "$PR_URL"
+name: Dependabot automerge
+on: workflow_call
+permissions: {}