https://docs.microsoft.com/en-us/rest/api/compute/virtualmachines/createorupdate#datadisk

Need to add disks to the DataDisk section.

Use the "ScratchAttached" value (this is being defined in #14291).

Each data disk maxes out at 1023 GB so we need to be able to attach multiple data disks if ScratchAttached > 1023 GB.

From documentation, the minimum fields seem to be "diskSizeGB" "createOption", "lun" and "vhd". May need to extend existing support garbage collecting unmanaged disks to collect data disks. May want to spread disks across multiple storage containers / storage accounts?

      "dataDisks": [
        {
          "diskSizeGB": 1023,
          "createOption": "Empty",
          "lun": 0,
          "vhd": {
            "uri": "http://{existing-storage-account-name}.blob.core.windows.net/{existing-container-name}/myDisk0.vhd" 
          }
      ]