Add support for handling SSE with 'event' entries

[sashirestela]

No description provided.

[sashirestela]

The approach should be extended to consider stream objects of different classes associated to multiple events.

[sashirestela]

Sending back objects of different types is fine but it is not enough, we are losing the event type that could be valuable for any client using this functionality. It'll be necessary to create a new class Event with two fields: name (String) and data (Object) to keep the full information.

So, the new return types for methods will be: CompletableFuture<Stream<Event>> and Stream<Event>.