refactor: remove mount logic in harvester

[FrankYang0529]

Solution:
LH introduces VolumeAttachment CRD after v1.5. It can automatically attach/detach volume when there is a request from LH API / controller / CSI. We can just leverage LH mechanism and remove our implementation.

Related Issue:
#4907

Test plan:

Setup

1. Create a 3-node harvester from this branch.
2. Setup backup-target.

Case 1: snapshot can work on a stopped VM.

1. Create a VM.
2. After the VM is ready, stop the VM.
3. Check VM volumes are detached.
4. Take a snapshot on the VM. The snapshot can be ready.

Case 2: restore a snapshot from detached volumes can work.

1. Follow Case 1.
2. Make sure VM volumes are detached.
3. Restore the snapshot to a new VM. The new VM can be ready.
4. Restore the snapshot to replace the old VM. The old VM can be ready.

Case 3: backup can work on a stopped VM.

1. Create a VM.
2. After the VM is ready, stop the VM.
3. Check VM volumes are detached.
4. Take a backup on the VM. The backup can be ready.

Case 4: race condition doesn't break VMBackup.

1. Create a VM.
2. After the VM is ready, stop the VM.
3. Check VM volumes are detached.
4. Take multiple backup on the VM in a short time. All backup can be ready.

Case 5: restore a backup from detached volumes can work.

1. Follow Case 3.
2. Make sure VM volumes are detached.
3. Restore the backup to a new VM. The new VM can be ready.
4. Restore the backup to replace the old VM. The old VM can be ready.

[WebberHuang1118]

LGTM, just a question for restore from VM snapshot, thanks.

[Vicente-Cheng]

LGTM, also tested all test cases related to the snapshot/backup.

[WebberHuang1118]

LGTM, all testing cases work as expected. Thanks.

[bk201]

LGTM!!

[FrankYang0529]

@mergify backport v1.3

[mergify]

backport v1.3

✅ Backports have been created

• Backport to branch v1.3 not needed, change already in branch v1.3

[FrankYang0529]

@mergify backport v1.2

[mergify]

backport v1.2

✅ Backports have been created

• #5854 refactor: remove mount logic in harvester (backport #4910) has been created for branch v1.2 but encountered conflicts