Refactor ackMode configuration to use JavaUtils pattern

Replace explicit null check and manual ackMode setting with the
JavaUtils.acceptIfNotNull() pattern for consistency with other
property configurations in the initializeContainer method.

This improves code readability and maintains a uniform style
throughout the property initialization logic.

Signed-off-by: gobeomjun <alap_u@naver.com>

Author: K-jun98

spring-kafka/src/main/java/org/springframework/kafka/config/AbstractKafkaListenerContainerFactory.java

@@ -456,13 +456,9 @@ else if (this.autoStartup != null) {
 				.acceptIfHasText(endpoint.getClientIdPrefix(), instance.getContainerProperties()::setClientId)
 				.acceptIfNotNull(endpoint.getConsumerProperties(),
 						instance.getContainerProperties()::setKafkaConsumerProperties)
-				.acceptIfNotNull(endpoint.getListenerInfo(), instance::setListenerInfo);
-
-		// Set ackMode if specified in endpoint (overrides factory default)
-		String ackMode = endpoint.getAckMode();
-		if (ackMode != null) {
-			properties.setAckMode(ContainerProperties.AckMode.valueOf(ackMode.toUpperCase()));
-		}
+				.acceptIfNotNull(endpoint.getListenerInfo(), instance::setListenerInfo)
+				.acceptIfNotNull(endpoint.getAckMode(), ackMode ->
+						properties.setAckMode(ContainerProperties.AckMode.valueOf(ackMode.toUpperCase())));
 	}
 
 	@Override