feature: Add action to create multiarch container

.github/workflows/30-pipeline-build-container-multi-arch.yml

@@ -0,0 +1,23 @@
+name: "Build Container Image: Multiarch"
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+    - name: Set up QEMU
+      uses: docker/setup-qemu-action@v3
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+    - name: Build multi-arch image and save as tar
+      run: |
+        docker buildx build \
+          --platform linux/amd64,linux/arm64 \
+          --output type=tar,dest=proxlb_image_multiarch.tar \
+          .
+    - name: Upload Docker image artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: proxlb-image-multiarch
+        path: proxlb_image_multiarch.tar