Clarify expected behaviour around EntityLinks when using WebFlux

[wilkinsona]

Thanks for the updates made for #1062, but I am still finding the documentation confusing as it seems to contradict itself.

In section 3.5, when talking about EntityLinks implementations it states that the "most fundamental one is ControllerEntityLinks that inspects SpringMVC and Spring WebFlux controller classes". Section 3.5.1 continues in the same vein. These sections are contradicted by section 3.5.3 where the update for #1062 means that the documentation now states that "EntityLinks and it’s various implementations are NOT currently provided out-of-the-box for Spring WebFlux applications".

Looking at the runtime behaviour, it seems to disagree with both of the documentation's opinions. Contrary to the update made for #1062, an EntityLinks instance is provided out-of-the-box when using Spring WebFlux applications and is available for dependency injection. However, when an attempt is made to use it in an @ExposesResourceFor-annotated controller, it fails:

java.lang.IllegalArgumentException: Cannot determine link for smoketest.hateoas.webflux.domain.Customer! No EntityLinks instance found supporting the domain type!
	at org.springframework.hateoas.server.core.DelegatingEntityLinks.lambda$getPluginFor$0(DelegatingEntityLinks.java:101) ~[spring-hateoas-1.0.0.GH1077-SNAPSHOT.jar:1.0.0.GH1077-SNAPSHOT]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	|_ checkpoint ⇢ org.springframework.web.filter.reactive.ServerWebExchangeContextFilter [DefaultWebFilterChain]
	|_ checkpoint ⇢ HTTP GET "/customers/1" [ExceptionHandlingWebHandler]

[odrotbohm]

Good catch, Andy. Looks like the inconsistency stems from the different stages of docs refactoring we did. I'll remove all references to WebFlux from these sections and add a not in the intro of the section that WebFlux is currently not supported.

[odrotbohm]

I've also tweaked the configuration to only activate EntityLinks for WebMVC scenarios. We'll revisit the WebFlux support for 1.1.