refactor: remove mount logic in harvester (backport #4910)

[mergify]

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, #5853, #5841

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.

---

This is an automatic backport of pull request #4910 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of e25e153 has failed:

On branch mergify/bp/v1.2/pr-4910
Your branch is up to date with 'origin/v1.2'.

You are currently cherry-picking commit e25e153c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   pkg/api/volume/handler.go
	modified:   pkg/api/volumesnapshot/handler.go
	modified:   pkg/controller/master/backup/backup.go
	modified:   pkg/controller/master/backup/backup_status.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   pkg/controller/master/backup/restore.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[bk201]

LGTM, verify with test plans in the description.

[WebberHuang1118]

Verify with #5841, and it works without issue in my env.

LGTM, thanks.