Expose presence-penalty and frequency-penalty parameters for the OpenAI API

[inthewaterwheel]

I've found that the presence & frequency penalties are rather important in tasks related to rephrasing - as the agent tends to fail via repeating input verbatim otherwise.

These feel like useful API parameters to expose - I could perhaps put a PR up for this if this sounds good.

[lslunis]

@stuhlmueller @reppertj @CG80499 Thoughts?

[CG80499]

This would be really helpful. Although generally I get better results changing the temperature.