Documentation update for KafkaListenerContainerFactory

[sergey-morenets]

In what version(s) of Spring for Apache Kafka are you seeing this issue?

2.8.6(latest)

Describe the bug

The latest Spring Kafka documentation contains outdated information about KafkaListenerContainerFactory (two generic types):
https://docs.spring.io/spring-kafka/reference/html/

@Bean
public KafkaListenerContainerFactory<?, ?> kafkaJsonListenerContainerFactory() {
    ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
        new ConcurrentKafkaListenerContainerFactory<>();
    factory.setConsumerFactory(consumerFactory());
    factory.setMessageConverter(new JsonMessageConverter());
    return factory;
}

But the current version of KafkaListenerContainerFactory has only one generic type:
https://github.com/spring-projects/spring-kafka/blob/main/spring-kafka/src/main/java/org/springframework/kafka/config/KafkaListenerContainerFactory.java

public interface KafkaListenerContainerFactory<C extends MessageListenerContainer> {

To Reproduce

Expected behavior

Spring Kafka documentation should use only one generic type for KafkaListenerContainerFactory.

[garyrussell]

Thanks; cherry-picked to all supported branches.