Produce guidance for writers for documenting subscription and feature tier requirements, which are not the same

In order to increase consistency in how we write about subscription level requirements or feature tier requirements (even in a non specific way such as "you must have the appropriate subscription or feature tier"), we should create clear guidance with examples.

More context about how subscription levels and feature tiers work in the parent issue.

This should be not only documented, but also clearly shared with the writing team.