Add mode parameter to gallery format

[Sophivorus]

Hi! The gallery format (https://www.semantic-mediawiki.org/wiki/Help:Gallery_format) seems to have a parameter for every attribute of the tag except for the "mode" (https://www.mediawiki.org/wiki/Help:Images#Mode_parameter). If there some technical reason for this lack, or was it an overlook? In any case, it would be great to have it since the mode attribute is quite crucial to control how galleries look. Thanks!