Debug logging for requests to WebFlux-based Actuator endpoints does not identify the endpoint

[christophejan]

This PR just add toString method on spring-boot-actuator WriteOperationHandler and ReadOperationHandler :

1. for consistency with AbstractWebMvcEndpointHandlerMapping$OperationHandler#toString()
2. otherwise AbstractWebFluxEndpointHandlerMapping$WebFluxEndpointHandlerMethod#toString() is quite useless

[wilkinsona]

Without this change, log messages are like this:

2022-05-06 15:13:07.751 DEBUG 34391 --- [ctor-http-nio-3] .b.a.e.w.r.WebFluxEndpointHandlerMapping : [285cdf1d-2] Mapped to org.springframework.boot.actuate.endpoint.web.reactive.AbstractWebFluxEndpointHandlerMapping$ReadOperationHandler@1d3bc254

With these changes applied, the debug message is then like this:

2022-05-06 15:14:55.644 DEBUG 34520 --- [ctor-http-nio-2] .b.a.e.w.r.WebFluxEndpointHandlerMapping : [20c7a545-1] Mapped to Actuator web endpoint 'health'

With MVC, the log output already looks like this:

2022-05-06 15:17:38.702 DEBUG 34603 --- [nio-8080-exec-3] s.b.a.e.w.s.WebMvcEndpointHandlerMapping : Mapped to Actuator web endpoint 'health'

This will further the changes made in 8e86bca for #14292.

[wilkinsona]

@christophejan Thanks very much for making your first contribution to Spring Boot.

[christophejan]

@wilkinsona A much better argumentation than mine. Thank you !

ps : it's always a pleasure to read your point of view, alway precise, with clear explanation and vision. A lot of thanks !

[wilkinsona]

That's very kind of you to say, thank you. And thanks again for the PR!