owncloud/core

Change: Disallow various special usernames

Special names "avatars", "files_encryption", "files_external" and "meta" are
used for other purposes in ownCloud and are not valid usernames (UIDs).
Creating a user with any of these names is now disallowed.

https://github.com/owncloud/core/issues/32547
https://github.com/owncloud/core/pull/37268