Add/update OpenAI model parameters

[escesare]

Three changes to OpenAI model parameters

• Add suffix parameter to GPT Completion models (not available for ChatGPT)
• Add all other parameters to ChatCompletion models (stop, top_p, frequency_penalty, presence_penalty)
• Automatically determine max output tokens based on GPT model if max_tokens not specified
  • Currently, the user specifies max total tokens, and then max output tokens is automatically determined by deducting the prompt tokens. This is unintuitive because
    1. The user shouldn't have to keep track of the max total tokens for a given model
    2. The max_tokens parameter in OpenAI models refers to the max output tokens, not max total, so we're using the phrase ambiguously here
  • I suggest the following, depending on whether user specifies max_tokens:
  • If unspecified (max_tokens=None), automatically determine max total tokens based on model name and deduct prompt tokens
  • If specified, simply use max_tokens as the max output tokens (aligning with how the OpenAI model uses it).

I apologize I also shuffled some other stuff around for vanity, and now it's hard to undo. I can remove those superfluous changes if you prefer.

[monk1337]

Thanks for this Awesome PR. @eren23 Please review it, and let's merge it.

[eren23]

I now tested the examples we have with the changes you made, looks good to me now