GET /api/permissions/invite-group-ids

IDs of the permission groups holding a stored read (or read-write) grant on the collection of a shareable item (a dashboard or a question). The "invite someone to view" group picker lists all groups and uses these ids to mark the ones whose members can already see the item; the Administrators group has implicit access to everything and is never included. The Data Analysts group is omitted unless advanced-permissions is enabled. The ids are otherwise unfiltered. Superuser-only, like the invite action itself.