fixes #5242 - Keep user's attributes and group membership up-to-date even during subsequent logons

Building on top of https://github.com/theforeman/foreman/pull/1390 and https://github.com/theforeman/foreman/pull/1328, we will update user's attributes and group membership.

It is only done for users in AuthSourceExternal, even if group memberships from groups related to the AuthSourceExternal external groups are revoked from any user.