feat(module): add DVCR capacity alert

[fl64]

Description

Adds the D8VirtualizationDVCRInsufficientCapacityRisk alert to monitor DVCR storage in the d8-virtualization namespace.
Triggers when free space drops below 5GB or 20% of capacity.

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

Low storage in the DVCR prevents the creation of new images and disks.

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: module
type: feat
summary: Adds the `D8VirtualizationDVCRInsufficientCapacityRisk` alert to monitor DVCR storage. Triggers when free space drops below 5GB or 20% of capacity.