Add GitHub Actions workflow for Spotless formatting

.github/workflows/formatter.yml

@@ -0,0 +1,46 @@
+name: Apply Spotless Formatting
+
+on:
+  pull_request:
+    branches:
+      - main
+  push:
+    branches:
+      - main
+
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    concurrency:
+      group: ${{ github.workflow }}-${{ github.head_ref || github.ref_name }}
+      cancel-in-progress: true
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref || github.ref_name }}
+          fetch-depth: 0
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          java-version: '17'
+          distribution: 'temurin'
+          cache: maven
+
+      - name: Apply Spotless formatting
+        run: mvn spotless:apply
+
+      - name: Commit changes if any
+        run: |
+          git config --global user.name "github-actions[bot]"
+          git config --global user.email "github-actions[bot]@users.noreply.github.com"
+          git add .
+          if ! git diff --quiet --staged; then
+            git commit -m "Apply Spotless formatting"
+            git pull --rebase origin ${{ github.head_ref || github.ref_name }}
+            git push origin HEAD:${{ github.head_ref || github.ref_name }}
+          else
+            echo "No formatting changes to commit."
+          fi