postmarketOS support

[sr229]

Is your feature request related to a problem? Please describe.
This is a new issue (AFAIK).

Describe the solution you'd like
postmarketOS (pmOS) is a mobile-centric Linux distribution based on Alpine Linux intended to provide a fully-free operating system for mobile. pmOS has a generic installer for x86 machines that we can pull from the servers however it is xz-compressed so we might have to be a lil creative with using it.

Describe alternatives you've considered
Ventoy with VHD2ISO is a viable alternative but it's not a tenable solution at the moment.

Additional context
Images can be found here: https://images.postmarketos.org/bpo/edge/generic-x86_64/os-installer/20250502-0114/

More info about the device variant can be found here: https://wiki.postmarketos.org/wiki/Generic-x86_64_(Generic-x86_64)