ci: Use docker buildx and qemu to build ARM64 images

.github/workflows/cicd.yml

@@ -90,6 +90,13 @@ jobs:
     if: github.ref_type == 'tag'
     runs-on: ubuntu-latest
     steps:
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: arm64
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v1
       - name: "Login to Docker Hub"
         uses: docker/login-action@v1
         with:
@@ -105,6 +112,7 @@ jobs:
         uses: docker/build-push-action@v2
         with:
           context: .
+          platforms: linux/amd64,linux/arm64/v8
           push: true
           tags: |
             foxcpp/maddy:${{ github.ref_name }}