public void stopOnlyBrokers() {
        cluster.brokers().values().forEach(BrokerServer::shutdown);
        cluster.brokers().values().forEach(BrokerServer::awaitShutdown);
    }
Stop only the Kafka brokers (and not the KRaft controllers). This can be used to test Connect's functionality
when the backing Kafka cluster goes offline.
connect/runtime/src/test/java/org/apache/kafka/connect/util/clusters/EmbeddedKafkaCluster.java