Document how to the extensible configuration with annotation works for dependent resources

See it here for KDR:

https://github.com/operator-framework/java-operator-sdk/blob/main/operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/dependent/kubernetes/KubernetesDependentResource.java#L31-L34


Not sure where is the best places to document this, we might want to introduce some "guides" in our docs, that describes such individual topics.