Register a listener, which will be called when this SseBroadcaster closes a given event SseEventSink or
tries to write to a given SseEventSink that is already closed (either by client closing the connection
or by calling close() on the server side.
Register a listener, which will be called when an exception is thrown by a given SseEventSink
when this SseBroadcaster tries to write to it or close it.