Add multi arch image (#48)

Author: ferranbt

.github/workflows/docker-utils-release.yaml

@@ -29,6 +29,7 @@ jobs:
         with:
           context: .
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: |
             docker.io/flashbots/playground-utils:latest
             docker.io/flashbots/playground-utils:${{ github.sha }}