Allow some domain events to be processed within the current transaction and others to be processed after

[barsifedron]

One domain event might trigger many event handlers (ie: one handler creates
activity logs and the other sends emails or updates a counter). If handler1
and handler2 both listen to the same event, we might want handler1 to run
within the SAME jpa transaction as the caller (default behavior) but we might
also want handler2 to wait for the current transaction to be committed before
running (failure to send an email should not usually roll back successful
changes for example).