Adding support for ARM64 architecture on bare-metal with flatcar-linux

[Sadi-a]

Overview

As of now, flatcar-linux on bare-metal only supports the amd64 architecture since the "amd64-usr" string is hardcoded everywhere in the code. I would like to change this and create an optional variable, which would default to amd64, to let an user choose his architecture and make typhoon with flatcar-linux on bare metal compatible with the aarch64 architecture.

Motivation

I am currently working on an aarch64 cluster and would like to make some changes which would make typhoon with flatcar-linux on bare-metal compatible with the aarch64 architecture.

[dghubble]

Same as #1045. Without suitable arm64 hardware for me to vet features on, I can't add support in main. If you have arm64 hardware and want to tweak the options, I'd suggest doing that in a fork for now.

[Snaipe]

Rather than testing on hardware, wouldn't it make more sense to have a test suite that brings up both x86_64 and aarch64 VMs and tries to provision them separately? I've certainly been doing local testing this way with libvirt, and it seems it could be used to automate the testing of this repo.