DRIVERS-2797 Check for substring in Index Management error asserts

[kevinAlbs]

Summary

Check for substring in Index Management error asserts

Background & Motivation

Atlas Search Index specification tests expect an error returned from a non-Atlas server. Example:

        expectError:
          # This test always errors in a non-Atlas environment.  The test functions as a unit test  by asserting
          # that the driver constructs and sends the correct command.
          isError: true
          errorContains: Search index commands are only supported with Atlas

SERVER-83290 changed the error message from:

Search index commands are only supported with Atlas

to:

Using Atlas Search Database Commands and the $listSearchIndexes aggregation stage requires additional configuration. Please connect to Atlas or an AtlasCLI local deployment to enable. For more information on how to connect, see https://dochub.mongodb.org/core/atlas-cli-deploy-local-reqs

The message change causes this test to fail in driver tests with latest server builds.

This PR proposes using "Atlas" as a common substring in both errors.

Updated tests were verified in C driver:
https://spruce.mongodb.com/version/6581c5d12a60ed6df70bbe25

Rejected alternatives

Checking the server error code was considered as an alternative. The returned errorCode also appears to have changed.

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Please complete the following before merging:

• [ ] Update changelog. N/A.
• 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). Tested with replica set and sharded cluster. Tests are not run in C driver load balancer tasks