Add dependabot automerge workflow

This will ensure that minor/patch version changes will be automatically
merged, reducing the effort required to keep dependencies up to date

.github/workflows/automerge.yml

@@ -0,0 +1,26 @@
+name: Dependabot Auto Merge
+on: pull_request_target
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor == 'dependabot[bot]' || (github.event.pull_request.user.login == 'dependabot[bot]' && github.actor == 'gocardless-robot') }}
+    steps:
+      - name: Dependabot metadata
+        id: dependabot-metadata
+        uses: dependabot/[email protected]
+        with:
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
+      - name: Enable auto-merge for Dependabot PRs
+        if: |
+          steps.dependabot-metadata.outputs.update-type == 'version-update:semver-patch' || steps.dependabot-metadata.outputs.update-type == 'version-update:semver-minor'
+        run: |
+          gh pr merge --auto --squash "$PR_URL"
+          gh pr review --approve "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: '${{ secrets.PUSH_REPO_TOKEN }}'