Allow to customise JAXRS server in spring boot when using cxf-spring-boot-autoconfigure

when using cxf-spring-boot-autoconfigure (via cxf-spring-boot-starter-jaxrs) there is no way to customise JAXRS server when using component or class scan and with spring boot 2 the bean override is disable by default meaning it will throw an exception if there are multiple beans of the same type).

Idea is to use 

@ConditionalOnMissingBean(name = "jaxRsServerConfiguration")

on the auto configuration to allow customisation.