Don't merge it yet: I wasn't right in this refactoring. We shouldn't override user preference from parent context. Need revert previuos state of this method.
I was thinking to add Boot dependency from here, as far as it has some useful `Conditional` implementations, but then decided to leave it as is. 
And I've changed my mind about Boot pluging: after introducing `@EnableIntegration` we can simply contribute to Boot `IntegrationAutoConfigurer`, similar to https://github.com/spring-projects/spring-boot/blob/master/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/reactor/ReactorAutoConfiguration.java