Simplify logic for when log challenge for basic authenticator

[cwperks]

Description

This PR is a replacement for opensearch-project#5221 which simplifies the logic in the basic authenticator.

The goal is to only log this in valid scenarios. The following criteria needs to be met:

• Request has no Authorization header
• There is a challenging basic auth authenticator
• Request is not for the SAML authtoken endpoint (used in ACS flow) which does not accept an Authorization header (its the endpoint that accepts the XML assertion) and is used in the SAML flow.

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Bugfix

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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