Description of problem:
When a user creates a golden image PVC, they attach it to an OS.
Currently the storage size is empty and should be filled by the user.

Along with the PVC's name and namespace, the relevant template also contains the recommended storage size. 
This value should be be used as the default PVC size (editable).


Version-Release number of selected component (if applicable):
OCP 4.7, CMV 2.6

How reproducible:


Steps to Reproduce:
1. Create a PVC from the UI, select to attach it to an OS


Actual results:
Storage size is empty and should be filled by the user

Expected results:
Storage size should be taken from the relevant template.

Additional info:
Template relevant section:

   dataVolumeTemplates:
    - apiVersion: cdi.kubevirt.io/v1beta1
      kind: DataVolume
      metadata:
        name: ${NAME}
      spec:
        pvc:
          accessModes:
          - ReadWriteMany
          resources:
            requests:
              storage: 30Gi