[#1331] cli/tree: Add order flag to tree get-subtree

Added `--ordered` flag to sort output by ascending FileName.

Signed-off-by: Ekaterina Lebedeva <ekaterina.lebedeva@yadro.com>

cmd/frostfs-cli/modules/tree/root.go

@@ -49,6 +49,7 @@ const (
 	heightFlagKey = "height"
 	countFlagKey  = "count"
 	depthFlagKey  = "depth"
+	orderFlagKey  = "ordered"
 )
 
 func initCTID(cmd *cobra.Command) {