DEV: WM atlas: output metric_label in tmp folder
DEV: WM atlas: output metric_label in tmp folder

Former-commit-id: 7a8dde3084636eb5e0cbf7a1254946a730cd10e2
Former-commit-id: 7d7415e64871813d311228a96c7420b83ae0da7b
3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox,3324fr/spinalcordtoolbox