fix name uniqueness validation for subgroups
requested to merge 345-cannot-create-2-assets-assettype-with-the-same-name-in-different-groups-subgroups into master
[A venir] Mise en place de quotas sur nos instances GitLab. Plus d'information sur : https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
[Coming soon] Quotas installation on our GitLab instances. More information: https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565