[Suggestion] init_hooks run as user

Is your feature request related to a problem? Please describe. I'm always frustrated when I have to run su $USER -- cmd in init_hooks in distrobox assemble

Describe the solution you'd like Obviously a conventional way to execute init_hooks as the distrobox's user in the container obviously through distrobox-init

Describe alternatives you've considered As mentioned su $USER -- cmd in init hook but it's kinda depend on weird behavior like the $USER variable expanding in v1 but I remember most of the variable expansion doesn't on the v2 distrobox.ini file