Support custom OpenAI provider from config

[ItzCrazyKns]

@ItzCrazyKns please add a config file parameter instead of relying on the UX, there are other people giving the same issues

Originally posted by @TomLucidor in #475

[thesobercoder]

@ItzCrazyKns First, let me thank you for such a wonderful piece of software. One suggestion is to allow environment variables to override values in the config file. Committing the config file simplifies life, but having to include the keys in that file makes things difficult.

[TomLucidor]

@thesobercoder would be great for both, when the files can be used to hide keys while allowing remote/shared access.

[ItzCrazyKns]

Implemented in v1.10.0 RC3