Kafka Bootstep update

The commit here has been peeled off of !852 (merged) to keep all of the bootstep changes in their own MR. These changes revolve around keeping all logic that directly interacts with the Kafka producer objects in the bootstep itself, i.e. tasks will never directly interact with Kafka producers.

EDIT: Removed signals, so now the tasks will still interact directly with the producers when writing to the producer, but other interactions (e.g. the delivery callback) will be left in the bootstep.