SpringBoot Only allow io.micrometer.* classes to be used by code in org.springframework.boot.actuate

We have some dependencies in spring-boot-autoconfigure that have a transitive dependency on Micrometer. We should only depend on Micrometer in spring-boot-actuator and spring-boot-actuator-autoconfigure so let's add some rules to our Checkstyle import control to prevent accidental usage outside of Actuator.