[Feature Request] Chat overlay: "stick to bottom" only when already at the bottom

Description Currently, the chat overlay will automatically and always scroll to the bottom of the overlay, when the answer from the LLM is still streaming. While this is nice for short answers, it is very annoying for longer answers. You might want to start reading the start of the answer, while the bottom/end is still streaming (and might continue to do so for a little while). This is currently not possible. You cannot start to read the answer, if the result is still streaming. You need to wait for the answer to finish streaming, before you can scroll to its top and start reading. Instead, it would be nice, if the auto-scrolling only happens, when the scroll position is already at the bottom (or very close to it). If the user scrolls up, it should break/stop the auto scrolling behavior. This is the typical and common behavior for these kind of message timelines. I'd be happy to come up with a small PR for it, if this feature request is approved. <img width=&qu…