DRIVERS-2761 do not apply readConcern or writeConcern to search index commands

[kevinAlbs]

Summary

• Require not applying read and write concern to search index commands.
• Add unit and integration tests to ensure readConcern and writeConcern is not applied to search index commands.

Tests were run in the C++ driver in this PR: mongodb/mongo-cxx-driver#1055

Background & Motivation

This PR proposes adding tests to ensure each search index command does not include readConcern or writeConcern.

Unit tests apply a non-default readConcern and writeConcern to the collection:

# Set a non-default read and write concern.
uriOptions:
    readConcernLevel: local
    w: 1

Unit tests verify the command started event is checked:

# Expect no writeConcern or readConcern to be sent.
writeConcern: { $$exists: false }
readConcern: { $$exists: false }

The integration test is as an extra precaution to test against a live Atlas instance.

The C++ driver failed unit and integration tests prior to fixes applied in mongodb/mongo-cxx-driver#1055.

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Please complete the following before merging:

• Update changelog.
• Make sure there are generated JSON files from the YAML test files.
• Test changes in at least one language driver. Tested in C++
• Test these changes against all server versions and topologies (including standalone, replica set, sharded clusters, and serverless).

[vbabanin]

LGTM!