Add support for arm64 architecture

[AAWO]

Can you add arm64 architecture image?
This would allow for easy deployment on Raspberry Pi boards an other ARM-based computers which begin to gain popularity.

[dmohns]

This would be absolute great 🎉

Looks like it should be an easy task when using docker buildx, see https://docs.docker.com/build/building/multi-platform/#example

The build scripts seems to use docker build however. Not sure how hard it would be to migrate from docker build to docker buildx or if there are any unwatned side effects.