Missing capacity field in NodePublishVolumeRequest #583

Is your feature request related to a problem?/Why is this needed
NodePublishVolumeRequest does not have a field indicating the desired capacity of a request.
But the capacity would be quite helpful to expose local storage of the node.

Describe the solution you'd like in detail
Adding a new field CapacityRange capacity_range = 9; to NodePublishVolumeRequest.

Describe alternatives you've considered
It would be possible to look into another resource to read the capacity (Kubernetes persistent volume claims in my case). But that call would require additional permissions and additional calls.

Additional context
n/a

I could provide the required change :)