This simplifies the crawler-linkback-list to only be a point of reference to the actual DiscussionForumPosting objects.
See "Summary page": https://developers.google.com/search/docs/advanced/structured-data/carousel?hl=en#summary-page
> [It] defines an ItemList, where each ListItem has only three properties: @type (set to ListItem), position (the position in the list), and url (the URL of a page with full details about that item).
Ayke Halder
David Taylor
Phil Pirozhkov