[Goal] Refine visibility into each feature completeness and graduation readiness with minimal overhead

[whitneygriffith]

As of now, Istio uses these feature checklists to track the state of a feature that we aren't sure is the best way to track feature progression as yet as not all features have been added, PRs to update have been sitting for too long, etc.

• [ ] Review open PRs on Enhancements Repo #165