chore: add CODEOWNERS (managed by owncloud/admin)

Author: owncloud-settings-bot[bot]

.github/CODEOWNERS

@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: ownCloud GmbH - A Kiteworks Company and ownCloud contributors
+# SPDX-License-Identifier: Apache-2.0
+#
 # Managed by owncloud/admin — edit codeowners/ownership.yml, not this file.
 # Generated by scripts/sync-codeowners.py. Last matching pattern wins.
 * @owncloud/classic-maintainers