Add support for multi-arch containers

Create the kas and kas-isar containers also for arm64. This allows using
them for arm-native builds, e.g. in AWS instances.

We need to drop a couple of packages from arm64 images which do not
exist on that arch. If the kas image is usable for Yocto builds is
untested, though. The Isar image works.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

.github/workflows/next.yml

@@ -48,6 +48,10 @@ jobs:
     steps:
       - name: Check out repo
         uses: actions/checkout@v2
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
       - name: Login to ghcr.io
         uses: docker/login-action@v1
         with:
@@ -57,12 +61,14 @@ jobs:
       - name: Build kas image
         uses: docker/build-push-action@v2
         with:
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ghcr.io/siemens/kas/kas:next
       - name: Build kas-isar image
         uses: docker/build-push-action@v2
         with:
           file: Dockerfile.isar
+          platforms: linux/amd64,linux/arm64
           build-args: KAS_TAG=next
           push: true
           tags: ghcr.io/siemens/kas/kas-isar:next