[DOC] Encryption in transit for gRPC

[finnegancarroll]

What do you want to do?

• Add new documentation

Provide a new page under security > configuration > gRPC to document enabling encryption in transit for the gRPC transport which will GA select APIs in 3.2.

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
3.2

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
Feature PR: opensearch-project/security#5375