Clean up info about response data, place in table

What does this MR do?

As a follow-up to Begin revisions of merge requests API page (!102566 - merged), we now have a table for the response to the get single merge request endpoint. The next step is to take the random data points described in Single merge request response notes and build them into the response table, now that it exists.

I'll work on the info in the Merge status subheading in a parallel merge request. That's next up for me.

Related issues

• Related to Follow-up from "Introduce new detailed_merge_st... (#379607 - closed)
• Related to Introduce new detailed_merge_status to the merg... (!101724 - merged) where I made the decision to move this work to a follow-up
• Related to Introduce new detailed_merge_status to the API (#370856 - closed)

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