Use webhooks to receive real-time updates from the OpenAI API

It has an interesting note: `Currently, the time to first token you receive from a background response is higher than what you receive from a synchronous one. We are working to reduce this latency gap in the coming weeks.`

A webhook by nature has a latency anyway, but it seems like the latency is much longer than one would expected such that OpenAI has to add this note???

Congrats OpenAI on the launch, and glad to see it's Standard Webhooks[1] compatible!

1: https://www.standardwebhooks.com/