public KafkaSystemDescriptor withProducerBootstrapServers(List<String> producerBootstrapServers) {
    this.producerBootstrapServers = producerBootstrapServers;
    return this;
  }
A list of network endpoints where the Kafka brokers are running. This is given as a list of hostname:port pairs,
for example {@code ImmutableList.of("kafka1.example.com:9092", "kafka2.example.com:9092", "kafka3.example.com:9092")}.
It's not necessary to list every single Kafka node in the cluster: Samza uses this property in order to discover
which topics and partitions are hosted on which broker. This property is needed even if you are only consuming
from Kafka, and not writing to it, because Samza uses it to discover metadata about streams being consumed.

@param producerBootstrapServers network endpoints where the kafka brokers are running
@return this system descriptor
samza-kafka/src/main/java/org/apache/samza/system/kafka/descriptors/KafkaSystemDescriptor.java