Add: Leisure -> Movie Theaters -> Auditorium

[rajrao]

Currently movie theater has only the sub classes of Lobby and Food Court (https://github.com/openooh/venue-taxonomy/blob/main/specification-1.1-draft1.md#leisure-movie-theaters). It would be beneficial to add auditorium as a new item. I believe this is important as the auditorium can display ads that are of higher value and will typically be longer than ones shown in lobbies and food courts. Finally, this part of the spec requires one to use only child types, when they are present: "No screens should be solely assigned to a parent venue type, unless that parent venue type has no children."