ci: add dependabot dev automerge

.github/workflows/dependabot.yml

@@ -0,0 +1,36 @@
+name: Auto-merge Dependabot dev dependencies
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'dependabot[bot]' && github.repository == 'projectcaluma/ember-alexandria'
+    steps:
+      - name: Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+        with:
+          github-token: "${{ secrets.GITHUB_TOKEN }}"
+      - uses: actions/checkout@v4
+        if: steps.metadata.outputs.dependency-type == 'direct:development'
+      - name: Approve a PR if not already approved
+        if: steps.metadata.outputs.dependency-type == 'direct:development'
+        run: |
+            gh pr checkout "$PR_URL" # sets the upstream metadata for `gh pr status`
+            if [ "$(gh pr status --json reviewDecision -q .currentBranch.reviewDecision)" != "APPROVED" ];
+            then gh pr review --approve "$PR_URL"
+            else echo "PR already approved, skipping additional approvals to minimize emails/notification noise.";
+            fi
+        env:
+            PR_URL: ${{github.event.pull_request.html_url}}
+            GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
+      - name: Enable auto-merge for Dependabot PRs
+        if: steps.metadata.outputs.dependency-type == 'direct:development'
+        run: gh pr merge --auto --rebase "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GH_TOKEN: ${{secrets.GITHUB_TOKEN}}