The `GatewayProxyInstantiationPostProcessor` does nothing on the AOT phase.
Therefore, scanned and imported beans for `@MessagingGateway` are not decorated
after AOT
* Implement a `BeanRegistrationAotProcessor` in the `GatewayProxyInstantiationPostProcessor`
to `RegisteredBean.getMergedBeanDefinition()` withe respective `AnnotationGatewayProxyFactoryBean`
and its requirements for ctor arg and `targetType`
* Scan for the `@MessagingGateway` bean in the `GatewayProxyInitializationAotProcessor`
to register respective proxy hints
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