Restrict invite permissions to user

Hi,

Looking to set up an instance with a single "superuser" that can create organisations and invite users to them. Signups should not be allowed by any other means. I would like for users to be able to create collections within their organisations, but that requires the admin role, which includes invite permissions.

I would therefor like to see a variable controlling who is allowed to send invitations, similar to the org_creation_users variable.

I learned that you can invite users via the admin panel, even when invitations are disabled globally, but that is not ideal.