Add missing file

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

lib/public/User/Backend/ICountMappedUsersBackend.php

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright Copyright (c) 2022 Côme Chilliet <come.chilliet@nextcloud.com>
+ *
+ * @author Côme Chilliet <come.chilliet@nextcloud.com>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCP\User\Backend;
+
+/**
+ * @since 26.0.0
+ */
+interface ICountMappedUsersBackend {
+	/**
+	 * @since 26.0.0
+	 *
+	 * @return int The number of users already mapped to a Nextcloud account
+	 */
+	public function countMappedUsers(): int;
+}