User Story:
As an OpenShift Engineer I need to create a new feature gate and CRD changes for vSphere multi disk so that we can gate the new function until all bugs are ironed out.

Description: 
This task is to create the new feature gate to be used by all logical changes around multi disk support for vSphere.  We also need to update the types for vsphere machine spec to include new array field that contains data disk definitions.

Acceptance Criteria:
   - New feature gate exists for components to use.
   - Initial changes to the CRD for data disks are present for components to start using.