fix(core): report active vm migration progress

[danilrwx]

Description

Update migration progress semantics in images/virtualization-artifact so VM-facing status reflects that migration is already underway once target scheduling/preparation has started.

The change updates migration condition messages and adds tests for active-progress states in VM and VMOP controllers.

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

During live migration, the target pod can already be created or scheduled and target preparation can already be running, while the user still sees a pending/awaiting-start style status.

This is misleading because the migration workflow has already started. The PR makes these intermediate states look like active progress instead of waiting.

What is the expected result?

1. Start a VM migration.
2. When migration enters target scheduling / target preparation stages, observe VM migration status.
3. Verify that the message reports active progress instead of "awaiting start" or similar pending wording.
4. Verify unit tests cover the updated semantics.

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: core
type: fix
summary: "Improve VM migration progress reporting while target scheduling and preparation are already in progress."
impact_level: low