Disable volume size input when isLonghornV2 and edit mode

[a110605]

Summary

Disable volume size input when isLonghornV2 and edit mode

PR Checklist

• Is this a multi-tenancy feature/bug?
  • Yes, the relevant RBAC changes are at:
• Do we need to backport changes to the old Rancher UI, such as RKE1?
  • Yes, the relevant PR is at:
• Are backend engineers aware of UI changes?
  • Yes, the backend owner is: @tserong

Related Issue #
harvester/harvester#6791

Screenshot/Video

Create mode

Edit mode

[tserong]

LGTM, thanks!