Clarify and fix how bean naming/override works

[sdeleuze]

Currently in a few places we are invoking BeanDefinitionReaderUtils.uniqueBeanName() "manually" to generate a unique bean name in order to have multiple beans (see for example for having multiple routers here).

It would be nice to be analyze more closely what Spring Boot does

• Spring Boot by default prevents bean overriding (can be changed via spring.main.allow-bean-definition-overriding=true), we should probably do that as well to avoid silent issues.
• Maybe some differences come from the fact that we are not using the annotation infrastucture (for example AnnotationBeanNameGenerator or FullyQualifiedAnnotationBeanNameGenerator)
• There may be inconsistencies between Boot autoconfiguration but let's do our best for now by updating autoconfigure-adapter if needed, this will be fixed in a more structural way via #273.