https://kafka.apache.org/27/documentation/streams/developer-guide/
https://projectreactor.io/docs/kafka/release/reference/
https://www.baeldung.com/spring-boot-kafka-testing
reactor/reactor-kafka#183 reactor/reactor-kafka#108
https://spring.io/blog/2019/12/13/flight-of-the-flux-3-hopping-threads-and-schedulers