Make ConcurrentKafkaListenerContainerFactoryConfigurer Generic

[lipiridi]

Summary

This PR updates ConcurrentKafkaListenerContainerFactoryConfigurer to be generic, allowing it to configure any container factory instead of being limited to <Object, Object>.

Motivation

• Previously, the class was restricted to <Object, Object>, which prevented reuse for other container factories with different key/value types. Making it generic improves flexibility and reusability across various Kafka container configurations.
• This change also enables configuring programmatically created container factories using Kafka listener properties from application.yml, providing greater control and consistency in Kafka consumer setup.

[wilkinsona]

When we're reviewing this we should keep in mind #40174 and #19221. Both issues are related to Kafka auto-configuration and generics.

[snicoll]

Unfortunately, I am not sure that we should be making this change. The configurer is mostly for applying auto-configuration to custom container that are to be exposed for management of the ApplicationContext. I also wonder if the additional complexity is worth it given the primary goal of this class.

This PR doesn't introduce any tests and isn't actionable as such. Before you amend that, I'd like to better understand what you actually mean in the two motivations. Can you provide examples of both and show how the current class is relevant?

[lipiridi]

@snicoll thanks for your response!
We are currently creating container factories manually, but we want to configure them using spring.kafka.listener properties in a more convenient way, instead of writing boilerplate code.
Another risk is that the listener properties might be extended in the future, and we could miss these changes, failing to update the property injection code accordingly.

Here is the a real example of usage I'm trying to achieve:

@Configuration
@RequiredArgsConstructor
public class KafkaConfiguration {

    private final KafkaProperties kafkaProperties;

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, GenericRecord> buildFactory() {
        var buildProperties = this.kafkaProperties.buildConsumerProperties(null);

        DefaultKafkaConsumerFactory<String, Object> consumerFactory =
                new DefaultKafkaConsumerFactory<>(buildProperties, new StringDeserializer(), new ErrorHandlingDeserializer<>(new KafkaAvroDeserializer()));

        ConcurrentKafkaListenerContainerFactory<String, GenericRecord> factory =
                new ConcurrentKafkaListenerContainerFactory<>();

        ConcurrentKafkaListenerContainerFactoryConfigurer<String, GenericRecord> configurer = new ConcurrentKafkaListenerContainerFactoryConfigurer<>();
        configurer.setKafkaProperties(this.kafkaProperties);
        configurer.configure(factory, consumerFactory);

        return factory;
    }
}