Ticket 49230 - slapi_register_plugin creates config entry where it should not
    
    Bug Description:
        slapi-register-plugin systematically create an entry under
        'cn=plugins,cn=config' because it is not taking into account
        the flag 'add_entry in 'plugin_setup'.
    
        This is potentially a regression introduced by
        https://pagure.io/389-ds-base/issue/49066 (TBC)
    
    Fix Description:
        Test 'add_entry' before adding the entry
    
        https://pagure.io/389-ds-base/issue/49230
    
    Review by: Mark Reynolds, William Brown