Add GitHub Actions workflow for build & test

Author: barissayli

.github/workflows/build.yml

@@ -0,0 +1,27 @@
+name: Build & Test
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          java-version: '21'
+          distribution: 'temurin'
+
+      - name: Build customer-service
+        run: mvn -B clean verify
+        working-directory: customer-service
+
+      - name: Build customer-service-client
+        run: mvn -B clean verify
+        working-directory: customer-service-client