Upgrade oauth2-server to 8.0.0 version, rewrite repositories and entities, start rewriting tests. Intermediate commit [skip ci]

api/components/OAuth2/Keys/EmptyKey.php

@@ -0,0 +1,18 @@
+<?php
+declare(strict_types=1);
+
+namespace api\components\OAuth2\Keys;
+
+use League\OAuth2\Server\CryptKeyInterface;
+
+class EmptyKey implements CryptKeyInterface {
+
+    public function getKeyPath(): string {
+        return '';
+    }
+
+    public function getPassPhrase(): ?string {
+        return '';
+    }
+
+}