[DOCS] `related.*` field set usage

[ebeahan]

Overview

Create a usage section for the related.* field set.

Motivation

The intended use of the related.* fields isn't always straightforward, even with the existing descriptions. Take advantage of the usage section feature to provide detailed examples, like: https://gist.github.com/ebeahan/8cb6cd4e679114c09556449213f6ec96