namespace: add namespace label

in order to select namespace when convert nsnp to k8snp

Signed-off-by: Duan Jiong <djduanjiong@gmail.com>

pkg/constants/constants.go

@@ -34,6 +34,7 @@ const (
 	IngressControllerPrefix       = "kubesphere-router-"
 
 	WorkspaceLabelKey              = "kubesphere.io/workspace"
+	NamespaceLabelKey              = "kubesphere.io/namespace"
 	DisplayNameAnnotationKey       = "kubesphere.io/alias-name"
 	DescriptionAnnotationKey       = "kubesphere.io/description"
 	CreatorAnnotationKey           = "kubesphere.io/creator"