fix(api): make user-facing condition messages clearer

[fl64]

Description

Status conditions on virtualization resources sometimes described a problem in terms the user cannot see or act on — launcher and migration pods, storage volume claims, internal virtualization objects, image-registry internals — or used awkward, sometimes ungrammatical wording. This reworks the .status.conditions[].message texts across VirtualMachine, VirtualMachineBlockDeviceAttachment, VirtualDisk, VirtualImage, ClusterVirtualImage, VirtualDiskSnapshot and VirtualMachineSnapshot so each message describes the current state in terms of the resources a user actually works with.

Only the message wording changes. Condition types, reasons, statuses and all reconcile behaviour stay the same. This PR covers the text-only changes; messages that still relay a raw internal error will be cleaned up separately.

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

A user reads a resource's status to understand what is happening with it. When a VirtualMachine is stuck or a disk or image is not ready, a message that points at a pod, a storage volume claim or an internal object gives no actionable signal and exposes implementation details the user has no control over. Clear, self-explanatory messages let users troubleshoot on their own and read straight into the module's release notes.

What is the expected result?

kubectl describe on these resources shows user-facing wording, for example:

• Virtual disk "vd1" is waiting for its storage to be provisioned (was: … underlying PVC to be bound);
• Migration is in progress: preparing the migration target (was: … target pod is being scheduled and prepared);
• VirtualMachine "x" is not fully started yet (was: InternalVirtualizationVirtualMachineInstance "x" not found);
• The image is being imported (was: Import is in the process of provisioning to DVCR).

Behaviour is unchanged: reasons and statuses are the same, so anything that keys on them is unaffected.

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: vm
type: fix
summary: VirtualMachine status messages are clearer and no longer expose internal implementation details.
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section: vmbda
type: fix
summary: VirtualMachineBlockDeviceAttachment status messages are clearer and no longer expose internal implementation details.
---
section: vd
type: fix
summary: VirtualDisk status messages are clearer and no longer expose internal implementation details.
---
section: vi
type: fix
summary: VirtualImage status messages are clearer and no longer expose internal implementation details.
---
section: cvi
type: fix
summary: ClusterVirtualImage status messages are clearer and no longer expose internal implementation details.
---
section: vdsnapshot
type: fix
summary: VirtualDiskSnapshot status messages have clearer wording.
---
section: vmsnapshot
type: fix
summary: VirtualMachineSnapshot status messages have clearer wording.