Additional option to add and del operations can be set
    
    By setting the property 'additional_add_del_field' to the name of one of
    the fields which are on current details page, we choose field which value
    will be added to  *_add_* and *_del_* commands in this format:
    
    {field_name: field_value}
    --field_name: field_value
    
    Part of: https://fedorahosted.org/freeipa/ticket/5426
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>