cli: Adapt add-forge-now so it demos the unified use of 'instance'
(the add-forge-now cli has a --lister-instance-name flag)
Refs. swh-lister#4693
Edited by Antoine R. Dumont
Staging instance, all changes can be removed at any time
(the add-forge-now cli has a --lister-instance-name flag)
Refs. swh-lister#4693