Add ChatGPT to OpenAI module

The idea is:

Today OpenAI launched a new operation called Chat, and a model called gpt-3.5.

See post here: OpenAI API

Would love to have this new operation and model available inside a node.

My use case:

This would mean more complicated prompts and AI automation tools can be generated. Instead of having an AI only answer one thing, we can now use the chat API endpoint to provide more context and therefore smarter answers.

Oh I Sooooooooooooo need this! Beginning to hold responses within coda, and will use it as a visible memory store! Excited!!!

Work on this has started in this PR.