Fix fetch-images command (#55365)

pkg/build/cmd/main.go

@@ -135,6 +135,10 @@ func main() {
 				},
 			},
 		},
+		{
+			Name:  "artifacts",
+			Usage: "Handle Grafana artifacts",
+			Subcommands: cli.Commands{
 				{
 					Name:  "docker",
 					Usage: "Handle Grafana Docker images",
@@ -150,6 +154,8 @@ func main() {
 						},
 					},
 				},
+			},
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {