Add an option to choose the eventing model

[gsmet]

And bubble up the errors to HTTP response, if sync.

[gsmet]

There's one major drawback to the sync approach though: if you have several methods listening to the same event, an error will cancel the rest of the execution, which might not be practical.

That was one of the reasons why I went with the async approach.

I would have to use another approach than CDI observers for the sync case if we want to collect all errors and not stop the execution randomly.

[gsmet]

We won't pursue this.