Optionalinclude_If set, an additional chunk will be streamed before the data: [DONE] message.
The usage field on this chunk shows the token usage statistics for the entire
request, and the choices field will always be an empty array.
All other chunks will also include a usage field, but with a null value.
NOTE: If the stream is interrupted, you may not receive the final usage
chunk which contains the total token usage for the request.
Options for streaming response. Only set this when you set
stream: true.