Add "Related content" as the final section in most pages

[stevepiercy]

As an example, the MS SQL docs have "Related content" as the final section in most of their pages.

https://learn.microsoft.com/en-us/sql/t-sql/queries/at-time-zone-transact-sql?view=sql-server-ver17#related-content

I think something like this would be a nice enhancement for the future docs structure.

Originally posted by @stevepiercy in https://github.com/plone/volto/pull/7360#discussion_r2367018720