Allow cross-namespace restore of CSI snapshots

- Check for namespace mapping information.
- If there is a map, replace VolumeSnapshots namespace to the target namespace

Fixes KUBEDR-364 and KUBEDR-406

Fixes Issues these similar issues from Velero:
1. vmware-tanzu/velero#2143
2. https://github.com/vmware-tanzu/velero-plugin-for-csi/issues/75

internal/restore/pvc_action.go

@@ -146,6 +146,12 @@ func (p *PVCRestoreItemAction) Execute(input *velero.RestoreItemActionExecuteInp
 		pvc.SetNamespace(val)
 	}
 
+	// If cross-namespace restore is configured, change the namespace
+	// for PVC object to be restored
+	if val, ok := input.Restore.Spec.NamespaceMapping[pvc.GetNamespace()]; ok {
+		pvc.SetNamespace(val)
+	}
+
 	volumeSnapshotName, ok := pvc.Annotations[util.VolumeSnapshotLabel]
 	if !ok {
 		p.Log.Infof("Skipping PVCRestoreItemAction for PVC %s/%s, PVC does not have a CSI volumesnapshot.", pvc.Namespace, pvc.Name)