Forking from discussion on #6739

We should be able to set environment vars for service information using the downward API mechanism from #6739. Since services are not local to the object, we need a way to specify them in the API. How about:

type EnvVarSource struct {
  FieldPath        *ObjectFieldSelector
  ServiceFieldPath *NamedObjectFieldSelector
}

type NamedObjectFieldSelector {
    ObjectFieldSelector

    Name string
}

This will definitely lurch us closer to a full ObjectReference.

@thockin @bgrant0607 @smarterclayton