Add @rev-robotics/rev-hub-core package when we add Control Hub support

[NoahAndrews]

The core package will be source of truth of the RevHub interface as well as all interfaces that extend RevHub. This will allow a ControlHub to have ExpansionHub children without having to depend on the expansion-hub package, which would introduce a needless transitive dependency on RHSPLib (Expansion Hubs that are children of Control Hubs will be communicated with via WebSocket, from the perspective of our libraries).