Add auto-approve and auto-merge for Dependabot PRs (frequenz-floss#211)

Uses our own fork.

Author: Marenz

.github/workflows/auto-dependabot.yaml

@@ -0,0 +1,17 @@
+name: Dependabot Auto Manage
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: github.actor == 'dependabot[bot]'
+    steps:
+      - uses: frequenz-floss/dependabot-auto-approve@v1
+        with:
+          dependency-type: 'all'
+          auto-merge: 'true'
+          add-label: 'auto-merged'