Enable milestone key dates in epic & enable to be used in custom roadmap

Our team uses releases by a timeframe, not by an individual product release. Thus our release is made up of multiple epics that need a milestone per epic. Please enable a milestone option at the epic level in both the epic & custom roadmaps to enable us to use this amazing functionality for custom roadmaps for leadership.

Currently our team needs to manage this via a dummy feature which creates all kinds of confusion and doesn't display different than any other feature in the roadmaps.