This PR introduces the possibility of inviting new users with an `admin`
role and changing the role of already invited users.
Also using scoped permission checks where applicable instead of using
user role checks.
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Co-authored-by: Val <68596159+valya@users.noreply.github.com>
Co-authored-by: Alex Grozav <alex@grozav.com>
Co-authored-by: Iván Ovejero <ivov.src@gmail.com>
