[DOC] Create documentation for Client Side Encryption in OpenSearch

[ashking94]

This is a placeholder for documentation addition/update that we will be required as part of opensearch-project/OpenSearch#6353.

What do you want to do?

• 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 and all versions that are affected.
As part of feature proposal of Client Side Encryption in OpenSearch, this will assist in documentation of the same.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[ashking94]

Closing since #2995 has been created.