feat: add Role (owner|admin) to the user domain, persistence model and mapper

api/pkg/apperr/messages.go

@@ -21,4 +21,5 @@ const PendingInviteErrorMessage = "There's already a pending invite for this add
 const InviteNotSentErrorMessage = "Couldn't send the invite. Try again in a moment."
 const InviteInvalidErrorMessage = "This invite link doesn't work."
 const InviteExpiredErrorMessage = "This invite has expired."
+const OwnerRequiredErrorMessage = "Only the owner can do this."
 const UsernameTakenErrorMessage = "That username is taken. Try another."