feat(API): optional display name on users

internal/domain/user/userRepositoryInterface.go

@@ -14,4 +14,5 @@ type Repository interface {
 	UpdatePasswordResetCode(userId uint32, code string, expiration time.Time) (User, error)
 	ClearVerificationCode(userId uint32) (User, error)
 	ResetPassword(userId uint32, hashedPassword string) (User, error)
+	UpdateDisplayName(userId uint32, displayName string) (User, error)
 }