Be able to toggle event to send

[shawnzhu]

Now

it emit all 3 events (QueryCreatedEvent, QueryCompletedEvent and SplitCompletedEvent) to kafka topic.

Expectation

It should provide config option like:

event-stream.querycompletedevent=true
event-stream.querycreatedevent=true
event-stream.splitcompletedevent=true

if any of the above value is false, it won't emit the very event into kafka topic.