Add an event that triggers on chat iterator consumption

Using magic method will not work, because there is limited time for processing after destruct, so a method needed to be added instead.

There is a merge request is here: https://git.drupalcode.org/project/ai/-/merge_requests/295

An OpenAI implementation is here: https://git.drupalcode.org/project/ai_provider_openai/-/merge_requests/4

It has graceful fallback in that it will not break the current streaming implementations, but they will need to use two methods to be able to trigger the event that is needed to log this.

A solution for the AI Logging is in there as well.

I can confirm that AI CKEditor logs the response correctly now when using MRs https://git.drupalcode.org/project/ai/-/merge_requests/295 and An OpenAI implementation is here: https://git.drupalcode.org/project/ai_provider_openai/-/merge_requests/4