Allow starting kwin_wayland as root

Running a Plasma Wayland session as root is not insecure, it is in fact the
opposite. There is no way for other users to somehow influence this session
due to the user separation and the user is more likely to only use this for
administrative actions. This is in contrast to regular user sessions, which
most likely start a mix of unprivileged programs next to privileged windows
like some with authorized kauth helpers or even just sudo in a konsole tab.