Missing envs for OpenAI compatible endpoints

[pseudotensor]

https://docs.openwebui.com/getting-started/env-configuration/

This has a nice collection of envs. For many purposes, these three are missing:

AUDIO_GENERATION_ENGINE: Can't set, so have to manually to go settings and change to OpenAI instead of default web API.

AUDIO_GENERATION_VOICE: Can't set, so have to manually to go settings and change to voice the OpenAI compatible endpoint supports (since different than real OpenAI).

OPENAI_API_USER: In many cases a user is required to be passed when in production environment for various OpenAI compatible endpoints like chat completion, image generation, embeddings. This should be passed as user= for those API calls.