public String bootstrapServers() {
        return String.join(",", getList(BOOTSTRAP_SERVERS_CONFIG));
    }
@return the {@link CommonClientConfigs#BOOTSTRAP_SERVERS_CONFIG bootstrap servers} property
used by the worker when instantiating Kafka clients for connectors and tasks (unless overridden)
and its internal topics (if running in distributed mode)
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/WorkerConfig.java