Allow passing a known key to Vault encrypt/decrypt functions

[hexedpackets]

Description

This lets an application cache a data key and use it for multiple operations without having to call the Vault API each time.

Documentation

Does this require changes to the WorkOS Docs? E.g. the API Reference or code snippets need updates.

[ ] Yes

If yes, link a related docs PR and add a docs maintainer as a reviewer. Their approval is required.