This avoids using a public global variable. It allows us to initialize
the default client a bit later (outside of init()). That way we can e.g.
properly initialize the in-memory registry.
* Use go-micro store to cache the roles
Add custom in-memory implementation
* replace redis with custom etcd implementation
* adjust table name for the cache in the roles manager
* Fix tests
* Fix sonarcloud issues
* Refactor for sonarcloud
* Allow configuration of cache per service
* Reuse parent context in etcd implementation
