Make clear what "Context Commits" are

What does this MR do and why?

What: This is the smallest possible change to mention the words "Context Commits" in the docs. Context Commits are equivalent to "previously merged commits".

Why:

• Currently there's no way to tell what a "Context Commit" is except by looking into the code, which isn't great. I got confused by this in #466153 (comment 1945030576).
• This term is only used in the API docs, but isn't defined anywhere.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.