Use OpenAI API client

[zurawiki]

Today, we use a naive HTTP request to get the OpenAI completions using the reqwest library.

Some benefits of a better API client

• Better handling around rate limits
• Typed parameters like model name and temperature
• We can better re-use connections (today we create HTTP client per completion)

We should use a more robust API client library. I saw a few choices on lib.rs: https://lib.rs/search?q=openai but there isn't any library that is officially supported by OpenAI

async-openai https://lib.rs/crates/async-openai looks promising but isn't v1

[zurawiki]

Closed, using async-openai's library