WebUI: Fix error "unknown command 'idoverrideuser_add_member'"
    
    There was wrong IPA.associator class used for 'Groups' -> 'User ID overrides' association,
    as a result a wrong command was sent to the server.
    
    Ticket: https://pagure.io/freeipa/issue/8416
    
    Signed-off-by: Serhii Tsymbaliuk <stsymbal@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>