Kafka 2.8 drops zookeeper

Hello,
Confluent recently announced Kafka 2.8 which is going to have a self-managed quorum system (see https://www.confluent.co.uk/blog/kafka-2-8-0-features-and-improvements-with-early-access-to-kip-500/#kip-500).

So for people using the latest kafka versions, the requirement to use zookeeper for burrow becomes redundant.
Also worth mentioning that confluent cloud does not provide access to zookeeper itself either.

No files, tests, or entry points are named. Start by tracing how Burrow currently depends on ZooKeeper, then define the required behavior for Kafka 2.8's self-managed quorum and Confluent Cloud; done means Burrow works without direct ZooKeeper access.

Written by the indexing model from the issue text.