KEYCLOAK-1534 handle account management update email or username to the already existing value

forms/common-themes/src/main/resources/theme/base/account/messages/messages_en.properties

@@ -109,6 +109,9 @@ invalidPasswordExistingMessage=Invalid existing password.
 invalidPasswordConfirmMessage=Password confirmation doesn''t match.
 invalidTotpMessage=Invalid authenticator code.
 
+usernameExistsMessage=Username already exists.
+emailExistsMessage=Email already exists.
+
 readOnlyUserMessage=You can''t update your account as it is read only.
 readOnlyPasswordMessage=You can''t update your password as your account is read only.