Phase 1 general gradual production rollout (71% -100%)

Context

This is part of the work to upgrade and migrate the GitLab.com container registry to a new version backed by a metadata database and online garbage collection (&5523 (closed)). This will be achieved following the gradual migration plan detailed in #374 (closed).

See &6872 (closed) for additional details.

Task

Perform the Phase 1 (new container repositories) general percentage-based rollout from 71% to 100% (inclusive).