actuator WebFluxTags#uri() cannot access other server's handlerMapping leads to tag explosion

[youzipi]

I have two server z-admin and z-gateway.
all request is sent to z-gateway and then dispatch to other servers (z-admin, ... )

In org.springframework.boot.actuate.metrics.web.reactive.server.WebFluxTags#uri,
the gateway cannot access the HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE，as it is on z-admin. so it record the full path with path variable to the tag.

I found this commit:
Avoid unbounded metrics creation for requests not handled by Spring MVC
But the nomapping seems not work in my situation

environment

<spring-boot.version>2.0.6.RELEASE</spring-boot.version>
<spring-cloud.version>Finchley.SR2</spring-cloud.version>

[bclozel]

Closing in favor of #15609.