Prevent Kafka sink from blocking

Previously, we used native Kafka sink implementation through kafka-clients.
This caused an issue when actual `send` operation becomes blocking as the
record write buffer fills and an actual send operation is performed.
We're currently successfully using fs2-kafka in enrich with Enrich without
major issues. Rewriting the Sink to use a two-effect pattern makes no sense
and therefore fs2-kafka is used to prevent blocking problems.

Author: peel