feat(API): optional display name on users

internal/infrastructure/persistence/repositories/userRepository.go

@@ -169,4 +169,20 @@ func (u *UserRepository) ResetPassword(userId uint32, hashedPassword string) (do
 	return mappers.UserToDomain(localUser), nil
 }
 
+func (u *UserRepository) UpdateDisplayName(userId uint32, displayName string) (domainUser.User, error) {
+	var localUser entity.User
+	err := u.db.Model(&entity.User{}).First(&localUser, userId).Error
+	if err != nil {
+		return domainUser.User{}, mapNotFoundErr(err, domainUser.ErrUserNotFound)
+	}
+
+	localUser.DisplayName = displayName
+	err = u.db.Save(&localUser).Error
+	if err != nil {
+		return domainUser.User{}, err
+	}
+
+	return mappers.UserToDomain(localUser), nil
+}
+
 var _ domainUser.Repository = &UserRepository{}