reuse: add SPDX headers to PHP source files, templates, and JS/CSS

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: szaimen <42591237+szaimen@users.noreply.github.com>

php/src/Controller/ConfigurationController.php

@@ -1,4 +1,7 @@
 <?php
+// SPDX-FileCopyrightText: 2021 Nextcloud GmbH <https://nextcloud.com>
+// SPDX-License-Identifier: AGPL-3.0-only
+
 declare(strict_types=1);
 
 namespace AIO\Controller;