fix(vi): unlock pending vi from vd ref

[LopatinDmitr]

Description

• A new "Employed" condition has been added to the VirtualDisk resource, which signals when the disk is attached not just to any VirtualMachine, but specifically to a VirtualMachine in the Running phase.
• The functionality of the VirtualImage controller has been fixed for creating images from a VirtualDisk that is attached to a running VirtualMachine.

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

What is the expected result?

Checklist

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