add username migration

database/migrations/data/20230923_1905_username.php

@@ -0,0 +1,20 @@
+<?php
+
+use MapGuesser\PersistentData\Model\User;
+use MapGuesser\Repository\UserRepository;
+use MapGuesser\Util\UsernameGenerator;
+use SokoWeb\Database\Query\Select;
+
+$select = new Select(Container::$dbConnection);
+$users = Container::$persistentDataManager->selectMultipleFromDb($select, User::class);
+$userRepository = new UserRepository();
+$usernameGenerator = new UsernameGenerator();
+
+foreach ($users as $user) {
+    do {
+        $username = $usernameGenerator->generate();
+    } while ($userRepository->getByUsername($username));
+
+    $user->setUsername($username);
+    Container::$persistentDataManager->saveToDb($user);
+}

database/migrations/structure/20230923_1905_username.sql

@@ -0,0 +1,3 @@
+ALTER TABLE `users`
+  ADD `username` VARCHAR(255) CHARACTER SET ascii COLLATE ascii_bin DEFAULT NULL AFTER `email`,
+  ADD UNIQUE `username` (`username`);