fix(vd): respect user-specified storage class when restoring from snapshot

[loktev-d]

Description

Fix the VirtualDisk controller to respect user-specified storageClassName when creating disks from VirtualDiskSnapshot. Previously, the controller was always using the storage class from the original disk (stored in VolumeSnapshot annotations), completely ignoring the user-specified value in spec.persistentVolumeClaim.storageClassName. Also add error message when user tries to perform cross-provider restore.

Why do we need it, and what problem does it solve?

When users tried to restore a VirtualDisk from a snapshot with a different storage class, the parameter spec.persistentVolumeClaim.storageClassName was silently ignored. The restored disk would always use the same storage class as the original disk.

What is the expected result?

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vd
type: fix
summary: respect user-specified storage class when restoring from snapshot

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[hardcoretime]

Can this statement be a problem if the target storage class has a different provisioner than the original?
For example, a volume snapshot is created with the original storage class, but after snapshotting, the original storage class is replaced by another storage class with the same name but a different provisioner.