Support roles in ChatCompletion

[half0wl]

https://platform.openai.com/docs/guides/chat/introduction

Currently, all prompts are sent as role=user. The endpoint supports (system, user, assistant) as roles.

I skipped this in the current version because it doesn't appear to be valuable - based on the docs and in my experience, the system role doesn't really affect model response.

[traosorus]

Check my repository on Betsy and test ChatbotAssistant.py . The system is counting with gpt turbo 3.5 and it's working quite well