Provide configurer for StreamsBuilderFactoryBean

[Vity01]

First of all, thanks for this great project. I really like it.
I dived into configuration problem.

At this time I don't see an easy way how to set additional properties for StreamsBuilderFactoryBean. uncaughtExceptionHandler or stateListener.
I can remove @EnableKafkaStreams to create custom StreamsBuilderFactoryBean instance (I cannot/I don't want to override beans since it's not recommended for Spring Core > 2.1) but I don't think it's a proper way to do it. I want to use inner code of StreamsBuilderFactoryBean initialization and also possible new bundled features of @EnableKafkaStreams in the future.
According to my experience the correct way to handle it is some "StreamsBuilderFactoryConfigurer"
(similar to well known WebSecurityConfigurerAdapter) where I can update FactoryBean before any StreamsBuilder is being instantiated.
There is also
KafkaStreamsFactoryBeanConfigurer in org.springframework.boot.autoconfigure.kafka.KafkaStreamsAnnotationDrivenConfiguration but it's not reusable for users...

I hope I described problem properly, let me know if there is something unclear.

[garyrussell]

We can certainly do that (and will) but I think we will defer it to 2.3 because there is a simple workaround you can use today...

@Bean
public static BeanPostProcessor bpp() {
	return new BeanPostProcessor() {

		@Override
		public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
			if (bean instanceof StreamsBuilderFactoryBean) {
				StreamsBuilderFactoryBean fb = (StreamsBuilderFactoryBean) bean;
				fb.setStateListener((newState, oldState) -> {
					System.out.println("State transition from " + oldState + " to " + newState);
				});
			}
			return bean;
		}

	};
}

[Vity01]

Thank you.