Document how to use cloudfoundry specific actuators with a custom base path for webflux applications

[mcordeiro73]

This issue is similar to #9081. When setting the spring.webflux.base-path, the Cloudfoundry specific actuators are also set under the configured base-path.

Looking for a workaround that allows the property to be set while relocating or redirecting the expected Cloudfoundry requests to the appropriate Actuators.

[mbhave]

We documented this as a known limitation for the servlet case and we should do the same for the webflux case.