Identify alternative approaches to building rest client when setting up SecurityRestTestCase

[DarshitChanpura]

Description

The sanity tests currently use OpenSearchRestTestCase.java to set up the client information to be used to test REST API calls against a remote cluster. This requires the client to be setup before the test executes. This hampers our ability to test with different clients.
Investigate better alternatives, if any, to prevent this.

What is expected?

If an alternative is found, a follow-up issue to be filed to make the changes. If none found, close this issue with an explaining comment.

[peternied]

[Triage] thanks for filing, this would be a good improvement