[DOC] gRPC JWT Support

[finnegancarroll]

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
Document support for JWT over gRPC transport/

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
3.5

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/security#5812
opensearch-project/security#5916