[Feature Request] Support docker build in qmk_userspace repos

[sotte]

Feature Request Type

• Core functionality
• Add-on hardware support (eg. audio, RGB, OLED screen, etc.)
• Alteration (enhancement/optimization) of existing feature(s)
• New behavior

Description

The main qmk_firmware repository provides the handy "build via docker" features.
Here are the docs: https://docs.qmk.fm/getting_started_docker
Here is the implementation: https://github.com/qmk/qmk_firmware/blob/master/util/docker_build.sh

It would be great if qmk_userspace also supported ''build via docker", especially now that userspace repos are encouraged and layouts are being removed from the main repo.

The github actions of qmk_firmware basically do something along the lines already, but you cannot easily reproduce it locally. (Here is the code of the action.)

Note: this is a crosspost to get more eyes. Feel free to close the less relevant ticket.