Add basic subuser listing for servers

app/Http/Requests/Api/Client/Servers/Subusers/GetSubuserRequest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Pterodactyl\Http\Requests\Api\Client\Servers\Subusers;
+
+use Pterodactyl\Http\Requests\Api\Client\ClientApiRequest;
+
+class GetSubuserRequest extends ClientApiRequest
+{
+    /**
+     * Confirm that a user is able to view subusers for the specified server.
+     *
+     * @return bool
+     */
+    public function authorize(): bool
+    {
+        return $this->user()->can('view-subusers', $this->route()->parameter('server'));
+    }
+}