It is nice to have webhook url property to run create parameter

Hi.

Current version, we need to the state of run with polling.
It may increase server and client resouce.

https://platform.openai.com/docs/api-reference/runs/createRun
It is nice to set webhook url to receive a message when the state changed.
Like below

curl https://api.openai.com/v1/threads/thread_abc123/runs \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H "Content-Type: application/json" \
  -H "OpenAI-Beta: assistants=v1" \
  -d '{
    "assistant_id": "asst_abc123"
    "webhook_url": "https://www.mydomain.com/webhook/openai"
  }'

The payload is good like that

{
    "assistant_id": "xxx",
    "thread_id": "xxxx",
    "state": "cancelling"
}

What do you think?