Add arm64 builds for Docker container (#25)

Builds both amd64 and arm64 containers on release.

Author: arbourd

.github/workflows/release.yml

@@ -23,6 +23,9 @@ jobs:
       - name: Docker set up buildx
         uses: docker/setup-buildx-action@v2
 
+      - name: Docker set up qemu
+        uses: docker/setup-qemu-action@v3
+
       - name: Docker login
         uses: docker/login-action@v2
         with:
@@ -35,5 +38,6 @@ jobs:
         with:
           context: .
           file: Dockerfile
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ghcr.io/grafana/xk6-client-tracing:latest,ghcr.io/grafana/xk6-client-tracing:${{ github.event.release.tag_name }}