Administrator to a group

❌ Issue

• When adding a new Administrator to a Group, the confirmation dialog is extremely simple and gives no indication to what's about to happen
• There's a trash can icon next to the Valider title that doesn't make sense when adding an administrator

✅ Expected

• Remove the trash can icon
• Change title Valider -> Confirmer le nouvel administrateur
• Change dialog message Êtes-vous sûr? -> Êtes vous sûr de vouloir ajouter cet utilisateur comme administrateur?
• Change confirmation button label Ok -> Ajouter un administrateur