Summary:
For users who cannot otherwise change access to a resource, let
them remove themselves. Implemented via the standard endpoints
as a special exception that will process a request from a user
that would otherwise be denied, if the only contents of that
request are a removal of themselves.
Users who can change access are still not permitted to change their
own permissions or to remove themselves, as a precaution against
orphaning resources.
Test Plan: extended and updated tests
Reviewers: cyprien
Reviewed By: cyprien
Subscribers: dsagal
Differential Revision: https://phab.getgrist.com/D3367
20dd2fc70d