Add batch publishing delay option in performance tool

Default in client is 100 ms, same in performance tool.

Adding the option provides more flexibility for workloads
with a low number of outstanding confirms.

Fixes #259

Author: acogoluegnes

src/main/java/com/rabbitmq/stream/perf/StreamPerfTest.java

@@ -17,6 +17,7 @@
 import static com.rabbitmq.stream.perf.Utils.ENVIRONMENT_VARIABLE_PREFIX;
 import static com.rabbitmq.stream.perf.Utils.OPTION_TO_ENVIRONMENT_VARIABLE;
 import static java.lang.String.format;
+import static java.time.Duration.ofMillis;
 
 import com.google.common.util.concurrent.RateLimiter;
 import com.rabbitmq.client.Channel;
@@ -203,6 +204,13 @@ public class StreamPerfTest implements Callable<Integer> {
       converter = Utils.PositiveIntegerTypeConverter.class)
   private int batchSize;
 
+  @CommandLine.Option(
+      names = {"--batch-publishing-delay", "-bpd"},
+      description = "Period to send a batch of messages in milliseconds",
+      defaultValue = "100",
+      converter = Utils.GreaterThanOrEqualToZeroIntegerTypeConverter.class)
+  private int batchPublishingDelay;
+
   @CommandLine.Option(
       names = {"--sub-entry-size", "-ses"},
       description = "number of messages packed into a normal message entry",
@@ -763,7 +771,10 @@ public Integer call() throws Exception {
                     }
 
                     String stream = stream(this.streams, i);
-                    ProducerBuilder producerBuilder = environment.producerBuilder();
+                    ProducerBuilder producerBuilder =
+                        environment
+                            .producerBuilder()
+                            .batchPublishingDelay(ofMillis(this.batchPublishingDelay));
 
                     String producerName = this.producerNameStrategy.apply(stream, i + 1);
                     if (producerName != null && !producerName.trim().isEmpty()) {