Add support for accepting/rejecting invites

Julian Sparberrequested to merge
jsparber/fractal:invites into fractal-next

This adds support for accepting/rejecting invites and the basework needed.

Mockup: https://gitlab.gnome.org/Teams/Design/app-mockups/-/blob/master/fractal/invites.png

Edited by Julian Sparber

Merge request reports