Geo: Enable Docker Registry replication by default

Problem to solve

Currently, replicating the Docker Registry is disabled by default https://docs.gitlab.com/ee/administration/geo/replication/docker_registry.html Should we turn on this feature by default? Does it even make sense?

Proposal

User experience goal

What is the single user experience workflow this problem addresses? For example, "The user should be able to use the UI/API/.gitlab-ci.yml with GitLab to " https://about.gitlab.com/handbook/engineering/ux/ux-research-training/user-story-mapping/

Pulling from a local secondary just works.