Make BroadcastHub only start pulling after atleast one Consumer attached to it?

[He-Pin]

Refs: akka/akka#28327

I just made a PR in akka/akka, which added a startAfterNrOfConsumers to BroadcastHub. And surely I will send the PR to pekko too.

I think we should make the current BroadcastHub.sink[T] with BroadcastHub.sink[T] = BroadcastHub.sink(startAfterNrOfConsumers = 1, defaultBufferSize) in pekko by default, which is 0 now.

[He-Pin]

I start the discussion in the email list, close now