Update documentation about support of direct JWKS with JWT

[Rishav9852Kumar]

Description

This PR adds comprehensive documentation for the new JWT JWKS (JSON Web Key Set) feature in OpenSearch 3.3, which enables direct JWKS endpoint support for JWT authentication without requiring OpenID Connect infrastructure.

What's New

• Direct JWKS Support: JWT authentication can now use JWKS endpoints directly via the new jwks_uri configuration parameter
• Automated Key Rotation: Dynamic key management through JWKS endpoints eliminates the need for manual key updates
• Enhanced Security: Built-in DoS protection with configurable rate limiting, timeouts, and response size restrictions
• Backward Compatibility: Existing static key configurations continue to work unchanged

Issues Resolved

opensearch-project/security#5578

Version

3.3 & above

Checklist

• By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin.
  For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[github-actions]

Thank you for submitting your PR. The PR states are In progress (or Draft) -> Tech review -> Doc review -> Editorial review -> Merged.

Before you submit your PR for doc review, make sure the content is technically accurate. If you need help finding a tech reviewer, tag a maintainer.

When you're ready for doc review, tag the assignee of this PR. The doc reviewer may push edits to the PR directly or leave comments and editorial suggestions for you to address (let us know in a comment if you have a preference). The doc reviewer will arrange for an editorial review.

[kolchfa-aws]

Thank you, @Rishav9852Kumar! Some wording suggestions before we can move to editorial review.

[kolchfa-aws]

Thank you, @Rishav9852Kumar! Some suggestions before we can move to editorial review.

[natebower]

Editorial review

[natebower]

LGTM