Feature request: allow alternative users for easier installs

[jscancella]

On the supplied BTT Manta image they already have installed klipper and mainsail. So it would be really nice to be able to reuse that user (biqu) instead of having to use a different image, create the pi user, and then use Kiuah to install everything under the pi user.

I think it would just involve changing https://github.com/Rat-OS/RatOS-configurator/blob/main/src/scripts/common.sh to not be hard coded to the pi user. If that is true I can work on a pull request to add that as a feature.

[jhorn70]

I am working on running setup.sh to get it installed on a minipc, I would be willing to assist witth this as well, or will basically end up doing it for my needs.