Updated workflow file main.yml and Makefile to handle building arm64 images

[shollingsworth]

• tested locally and in a runtime environment on a arm64 mac

This was the environment passed to it.

export VERSION=16-3.5
export ARCH="linux/arm64"
export VARIANT="alpine"

[phillipross]

Thanks for the contribution! I suspect this will need a deeper review, but I'm enabling CI runs to see what GHA does with it and give us a place to iterate.