ci: build also for arm64

Co-authored-by: kapdon <94782486+kapdon@users.noreply.github.com>

.github/workflows/build-tag.yml

@@ -13,6 +13,9 @@ jobs:
         with:
           username: ${{ vars.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Set up QEMU (for cross-arch)
+        uses: docker/setup-qemu-action@v3
       -
         name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -21,4 +24,5 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: webstreamr/webstreamr:latest