[Suggestion] Pre-defined voices for OpenAI

[NinjaPerson24119]

To use this with SillyTavern, it looks like I'm going to have to add a shim API over the provided one so that I can allow SillyTavern to pass the audio reference by name like "Voice1", rather than embed the audio over the request.

This is a common pattern for the server to provide a list of voices. It'd be cool if you could have the default behavior be able to look-up voice references from a predefined folder.