mesh-2092: add auto merge workflow

Author: james-bradley-nhs

.github/workflows/dependabot-auto-merge.yaml

@@ -0,0 +1,63 @@
+name: Auto-merge Dependabot PRs
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - ready_for_review
+      - labeled
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot-make-update:
+    # Only run on Dependabot PRs
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Install Python 3.11
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+
+      - name: Install poetry
+        run: python -m pip install --upgrade pip setuptools wheel poetry
+
+      - name: Install project dependencies
+        run: make install-ci
+
+      - name: Update dependencies (make update)
+        run: make update
+
+      - name: Lint (make lint)
+        run: make lint
+
+  enable-automerge:
+    # Only run on Dependabot PRs after make update succeeds
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    needs: dependabot-make-update
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@d7267f607e9d3fb96fc2fbe83e0af444713e90b7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for Dependabot PRs
+        if: steps.metadata.outputs.update-type == 'version-update:semver-patch'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}