Hide new status indicator by default through feature flag

Created by: mrnugget

After discovering that on instances with multiple thousands of repositories the new status indicator (#4120 (closed)) is nearly always active, we decided to hide this feature before branch cut to not confuse users.

In the meantime, I'll start work on figuring out how we can only show "cloning" progress. If that turns out to be "easy", we can cherry-pick into release branch or ship with point release.

Regarding the implementation of the feature flag itself, @dadlerj and @felixfbecker noted in Slack that it could also be implemented as a per-user feature flag through localStorage. That would mean it's not exposed to the user and not documented. I'm hoping for your input here, @christinaforney :)