ci: add dependabot auto-merge workflow for patch and minor updates

Auto-approves and enables auto-merge (squash) for dependabot PRs
that are patch or minor version bumps. Major version bumps still
require manual review.

Note: requires "Allow auto-merge" to be enabled in repo settings.

Author: tejaskash

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

@@ -0,0 +1,32 @@
+name: Dependabot Auto-Merge
+
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - name: Fetch Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+        with:
+          github-token: '${{ secrets.GITHUB_TOKEN }}'
+
+      - name: Auto-approve patch and minor updates
+        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
+        run: gh pr review --approve "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Enable auto-merge for patch and minor updates
+        if: steps.metadata.outputs.update-type != 'version-update:semver-major'
+        run: gh pr merge --auto --squash "$PR_URL"
+        env:
+          PR_URL: ${{ github.event.pull_request.html_url }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}