LDAP sync should update user's name

Zendesk: https://gitlab.zendesk.com/agent/tickets/69819

On LDAP sync (not to be confused with LDAP group sync), we update a user's email address, Kerberos identity, and SSH keys. We should also update the user's name if it has changed.

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/22924.