Add _search API endpoints to SRW documentation

[wrigleyDan]

Description

This PR adds the _search API endpoints of the Search Relevance Workbench to the documentation.

Issues Resolved

Closes #[Replace this text, including the brackets, with the issue number. Leave "Closes #" so the issue is closed properly.]

Version

3.5

Frontend features

n/a

Checklist

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[github-actions]

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[epugh]

A reminder to us: we need to highlight whihch fields are ignored automatically. We may want to add "and this is how you get control over what you want"....

[epugh]

@wrigleyDan once you give it a looksee, we need to tag the assigned person to move from technical to editorial review.

[wrigleyDan]

@kolchfa-aws Tech review is done, handing over to you for the next review steps.