Automatic merge from submit-queue (batch tested with PRs 51765, 53053, 52771, 52860, 53284). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Make feature gate enablement checks lock-free

Since we almost never write to this object after initial creation (basically, just in tests or during API server startup), this is a good candidate for the ["read mostly"](https://golang.org/pkg/sync/atomic/#example_Value_readMostly) pattern which leaves the reads lock-free