Rework tests structure. Upgrade codeception to 2.5.3. Merge params configuration into app configuration.

api/tests/_support/UnitTester.php

@@ -0,0 +1,12 @@
+<?php
+declare(strict_types=1);
+
+namespace api\tests;
+
+use api\tests\_generated\UnitTesterActions;
+use Codeception\Actor;
+
+class UnitTester extends Actor {
+    use UnitTesterActions;
+
+}