Improve docs about Acknowledgment.nack() (#2906)

Author: powibol

spring-kafka-docs/src/main/antora/modules/ROOT/pages/kafka/receiving-messages/message-listener-container.adoc

@@ -233,6 +233,8 @@ With a record listener, when `nack()` is called, any pending offsets are committ
 The consumer can be paused before redelivery, by setting the `sleep` argument.
 This is similar functionality to throwing an exception when the container is configured with a `DefaultErrorHandler`.
 
+IMPORTANT: `nack()` pauses the entire listener for the specified sleep duration including all assigned partitions.
+
 When using a batch listener, you can specify the index within the batch where the failure occurred.
 When `nack()` is called, offsets will be committed for records before the index and seeks are performed on the partitions for the failed and discarded records so that they will be redelivered on the next `poll()`.
 

spring-kafka/src/main/java/org/springframework/kafka/support/Acknowledgment.java

@@ -41,7 +41,9 @@ public interface Acknowledgment {
 	/**
 	 * Negatively acknowledge the current record - discard remaining records from the poll
 	 * and re-seek all partitions so that this record will be redelivered after the sleep
-	 * duration. Must be called on the consumer thread.
+	 * duration. This will pause reading for the entire message listener for the specified
+	 * sleep duration and is not limited to a single partition.
+	 * Must be called on the consumer thread.
 	 * <p>
 	 * @param sleep the duration to sleep; the actual sleep time will be larger of this value
 	 * and the container's {@code maxPollInterval}, which defaults to 5 seconds.