Add the option to see some "sensitive information" (username) in the log file

The nextcloud log is sometimes flooded with “OC\User\LoginException”, because of deactivated users or wrong passwords. The name of the user con not be found, independent what log level I activate. It’s always replaced by “*** sensiti … *” - it’s okay to remove the password, but the user name is essential to fix the issue or inform/help users.