add theme upgrade automation

Author: yyx990803

.github/dependabot.yml

@@ -0,0 +1,14 @@
+version: 2
+updates:
+  # Enable version updates for npm
+  - package-ecosystem: "npm"
+    # Look for `package.json` and `lock` files in the `root` directory
+    directory: "/"
+    # Check the npm registry for updates every day (weekdays)
+    schedule:
+      interval: "daily"
+    allow:
+      - dependency-name: "vue"
+      - dependency-name: "vitepress"
+      - dependency-name: "@vue/theme"
+      - dependency-name: "@vue/repl"

.github/workflows/automerge.yml

@@ -0,0 +1,23 @@
+name: Dependabot auto-merge
+on: pull_request
+
+permissions:
+  pull-requests: write
+  contents: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor == 'dependabot[bot]' }}
+    steps:
+      - name: Dependabot metadata
+        id: metadata
+        uses: dependabot/[email protected]
+        with:
+          github-token: '${{ secrets.GITHUB_TOKEN }}'
+      - name: Enable auto-merge for theme
+        if: ${{contains(steps.metadata.outputs.dependency-names, '@vue/theme') && steps.metadata.outputs.update-type != 'version-update:semver-major'}}
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}