Performance test the shipper Kafka output

[cmacknz]

Prior to considering the Kafka output available for beta use we should conduct some performance tests against a self-hosted or managed Kafka instance.

The initial goal of these tests is not to discover the optimal output configuration for publishing events to Kafka, but to perform an end to end test against a real Kafka instance and ensure that there are no obvious performance problems (e.g. throughput 25% as good as Elasticsearch without an obvious explanation).

We can base these tests off of the performance tests currently being designed with the Elasticsearch output using Filebeat as the shipper data source.