Review doFinally block in observability for chat models.

[markpollack]

Removing the following 'TODO' comment in public Flux<ChatResponse> stream(Prompt prompt) for various models.

.doOnError(observation::error)
				.doFinally(s -> {
					// TODO: Consider a custom ObservationContext and
					// include additional metadata
					// if (s == SignalType.CANCEL) {
					// observationContext.setAborted(true);
					// }
					observation.stop();
				})

[markpollack]

Seems like this was resolved as the TODO comments are no longer in the code.