[EC-95] Add job to build Docker image at PR validation for onboarding…

… ms (#108)

.github/workflows/pr_ms.yml

@@ -29,3 +29,28 @@ jobs:
       source_branch: ${{ github.head_ref }}
       target_branch: ${{ github.base_ref }}
       sonar_key: 'pagopa_selfcare-onboarding'
+
+  build_docker:
+    name: 'Build Docker image'
+    runs-on: ubuntu-20.04
+    permissions:
+      packages: write
+
+    steps:
+
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 #v4.1.1
+        name: Checkout
+
+      - name: Setup Docker buildx
+        uses: docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226 # v3.0.0
+
+      - name: Build Image
+        uses: docker/build-push-action@4a13e500e55cf31b7a5d59a38ab2040ab0f42f56 #v5.1.0
+        with:
+          context: .
+          file: ./apps/onboarding-ms/Dockerfile
+          push: false
+          secrets: |
+            GH_TOKEN=${{ secrets.READ_PACKAGES_TOKEN }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=min