rECAUaf893bc63d66: Set gu_auth_token when adding new users will populate gu_auth_token for all new users on creation, avoiding the need for CentralAuthUser->getAuthToken() to call CentralAuthUser->resetAuthToken(). However, this does not fix things for the existing users who do not have this field populated. To avoid various issues caused by these resetAuthToken() calls (e.g. T139970), we should run a maintenance script to fill the field after 1.28.0-wmf.11 is deployed everywhere.