Documentation for configuring custom `ConsumerFactory` and `ProducerFactory` beans when using Spring Boot is incorrect

[wilkinsona]

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

All supported versions.

Describe the bug

Please see spring-projects/spring-boot#40174.

To Reproduce

Please see spring-projects/spring-boot#40174.

Expected behavior

The custom consumer and or producer factories are used by the default listener container when following Spring Kafka's documentation. To achieve this the documentation should be updated to define the beans as ConsumerFactory<?, ?> and ProducerFactory<?, ?>.