ConsumerSeekAware default implementations

Add default method implementations to avoid users having to implement
methods they are not interested in.

spring-kafka/src/main/java/org/springframework/kafka/listener/ConsumerSeekAware.java

@@ -37,22 +37,28 @@ public interface ConsumerSeekAware {
 	 * containers listeners should store the callback in a {@code ThreadLocal}.
 	 * @param callback the callback.
 	 */
-	void registerSeekCallback(ConsumerSeekCallback callback);
+	default void registerSeekCallback(ConsumerSeekCallback callback) {
+		// do nothing
+	}
 
 	/**
 	 * When using group management, called when partition assignments change.
 	 * @param assignments the new assignments and their current offsets.
 	 * @param callback the callback to perform an initial seek after assignment.
 	 */
-	void onPartitionsAssigned(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback);
+	default void onPartitionsAssigned(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback) {
+		// do nothing
+	}
 
 	/**
 	 * If the container is configured to emit idle container events, this method is called
 	 * when the container idle event is emitted - allowing a seek operation.
 	 * @param assignments the new assignments and their current offsets.
 	 * @param callback the callback to perform a seek.
 	 */
-	void onIdleContainer(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback);
+	default void onIdleContainer(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback) {
+		// do nothing
+	}
 
 	/**
 	 * A callback that a listener can invoke to seek to a specific offset.

spring-kafka/src/test/java/org/springframework/kafka/annotation/EnableKafkaIntegrationTests.java

@@ -1689,18 +1689,6 @@ public void registerSeekCallback(ConsumerSeekCallback callback) {
 			this.seekCallBack.set(callback);
 		}
 
-		@Override
-		public void onPartitionsAssigned(Map<org.apache.kafka.common.TopicPartition, Long> assignments,
-				ConsumerSeekCallback callback) {
-			// NOSONAR
-		}
-
-		@Override
-		public void onIdleContainer(Map<org.apache.kafka.common.TopicPartition, Long> assignments,
-				ConsumerSeekCallback callback) {
-			// NOSONAR
-		}
-
 	}
 
 	interface IfaceListener<T> {