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

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.

[!CAUTION]
Pull requests that don't meet the following requirements shall be immediately closed.

1. The contributor should actually read and understand the content on both the page where they put the links and the destination pages of the links.
2. Ensure that the content between pages or sections is truly related. I've already seen and closed many PRs that mindlessly match a single word.
3. Not be on index.md pages. There's no content on index pages, so it's impossible for anything to be related to it.
4. Not be on pages that serve a similar function as index pages, such as a landing page that directs users to other pages.

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

No repository file or test is named. Start by reviewing the documentation structure and identifying eligible non-index pages, then use the stated contribution requirements to select genuinely related destinations. Done means appropriate pages have a final Related content section with meaningful links, without changing index or landing pages.