[blocker 2.4] NEXUS-5639: Deep rename of WL into Routing

Continues the "shallow" pull
https://github.com/sonatype/nexus/pull/794

This pull does a full rename of proxy404 related classes and APIs.

Changes:
* package from org.sonatype.nexus.proxy.maven.wl to org.sonatype.nexus.proxy.maven.routing
* classes got rid of WL references (somewhere just removed, somewhere replaced by Routing)
* proxy404 REST endpoints URL change (was /wl now is /routing)

CI
https://bamboo.zion.sonatype.com/browse/NXO-OSSF44-1

Note: this pull once merged will need to be propagated to other codebases using proxy404...