ARM Images slow to build on default runners

[scottyhq]

In #561 we started creating images for ARM platforms. I think it's known that using Docker QEMU is slow, but I didn't realize this would take 3-4x longer.

Anyways there are probably many ways to optimize this

• https://www.docker.com/blog/faster-multi-platform-builds-dockerfile-cross-compilation-guide/
• https://stackoverflow.com/questions/66337210/is-it-possible-to-push-docker-images-for-different-architectures-separately