Draft: postmarketos-backup

A GTK backup tool that uses APK to make backups quickly.

Currently here in temp/ for quick testing to make sure we don't push horribly broken backup software to alpine :)

To test this you'd basically have to sideload postmarketos-backup to an existing installation (since making backups of a brand new install is boring) then export the backup to SD, flash a new install on something, then import that backup and restore it