fix(vi): update CEL

[yaroslavborbat]

Description

update CEL for vi

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

Fix creating vi with pvc, dataSource for vi wtih pvc doen't required

Error: 1 error occurred:
        * VirtualImage.virtualization.deckhouse.io "performance" is invalid: [spec.dataSource: Required value, <nil>: Invalid value: "null": some validation rules were not checked because the object was invalid; correct the existing errors to complete validation]

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.