feat(ci): CI for automatic backend formatting on request (#2338)

* CI for automatic backend formatting on request

* intentionally misformat some code

* Automated backend code formatting

---------

Co-authored-by: Loculus bot <bot@loculus.org>

.github/workflows/format-backend-on-request.yml

@@ -0,0 +1,40 @@
+name: Format Backend Code
+on:
+  workflow_dispatch:
+  pull_request:
+    types: [synchronize, labeled]
+    paths:
+      - "backend/**"
+jobs:
+  format:
+    if: github.event_name == 'workflow_dispatch' || (github.event_name == 'pull_request' && contains(github.event.pull_request.labels.*.name, 'format_me'))
+    permissions:
+      contents: write
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
+
+      - name: Set up JDK
+        uses: actions/setup-java@v4
+        with:
+          java-version: "21"
+          distribution: "adopt"
+
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v3
+
+      - name: Format Backend Code
+        run: ./gradlew ktlintFormat
+        working-directory: ./backend
+
+      - name: Commit and Push Changes
+        run: |
+          git config --global user.name 'Loculus bot'
+          git config --global user.email 'bot@loculus.org'
+          git add -A
+          git commit -m "Automated backend code formatting" || echo "No changes to commit"
+          git push origin HEAD:${{ github.head_ref }}