use new Disposable.Composite to offer ParallelFlux#subscribe(lambda...) : Disposable

[smaldini]

Like this

@SuppressWarnings("unchecked")
		LambdaSubscriber<? super T>[] subscribers = new LambdaSubscriber[parallelism()];

		int i = 0;
		while(i < subscribers.length){
			subscribers[i++] =
					new LambdaSubscriber<>(onNext, onError, onComplete, onSubscribe);
		}


		onLastAssembly(this).subscribe(subscribers);
		return Disposable.composite(subscribers);