Build: Add linux/arm64 to docker build workflow (#648)

[gostega]

• Addresses issue Build docker image for Mac (arm64) #648
• Reference: https://docs.docker.com/build/ci/github-actions/multi-platform/

[janbrasna]

I'm not sure this is the only change needed for this to work. If you follow the instructions in the link posted in the description above, you'll notice the chapter describing QEMU setup, that the buildx step possibly needs to succeed in the runner. (See https://docs.docker.com/build/building/multi-platform/ for general info…) — My guess is that at least docker/setup-qemu-action to register the emulation types would be needed…?

[nabla-c0d3]

Thanks - I just merged it. No idea if this will work tho...