Feature: Add support for arm64 not-a-build-harness

[zack-is-cool]

The need for this feature came around due to iptables not working on emulated amd64 containers, this means that sshuttle won't function. sshuttle uses iptables + nft to configure the tunnel on linux.

I was running into this issue:
multiarch/qemu-user-static#191

After tweaking the dockerfile, I was able to locally build and runnot-a-build-harness as an arm64 container and was able to successfully use sshuttle and iptables commands.

docker buildx build --platform linux/arm64/v8,linux/amd64 -t not-a-build-harness:multiarch . --progress plain