doc: describe api/sql output + new parameters input

[sploiselle]

#11958 's first step is describing the desired output for api/sql, which this PR aims to do. Note that I have also added a number of issue links to #11958 to track the work necessary to bring our behavior in line with this doc.

cc @chaas @JLDLaughlin

Motivation

This PR describes known-desirable features.

Checklist

• [x] This PR has adequate test coverage / QA involvement has been duly considered.

• [ ] This PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way) and therefore is tagged with a T-protobuf label.

• [x] This PR includes the following user-facing behavior changes:

  • there are no user-facing behavior changes