public int probe() {
        List<CompletableFuture<Void>> futures = producers.stream()
            .map(Producer::probe)
            .flatMap(List::stream)
            .collect(Collectors.toList());
        CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).join();
        return futures.size();
    }
Send a message to each partition of each topic to ensure that the topic is created.
It throws an exception if any of the producers fail to send the message.
NOT thread-safe.

@return number of messages sent
tools/src/main/java/org/apache/kafka/tools/automq/perf/ProducerService.java