archwiki: rename archtu group to archpackager

Trusted Users are now called Package Maintainers.
See the discussion in https://wiki.archlinux.org/title/ArchWiki_talk:Requests#Trusted_User_name_change

Once this is deployed, the users need to be migrated to the new group
by running:

    php ./maintenance/migrateUserGroup.php archtu archpackager

Related to #533

roles/archwiki/templates/LocalSettings.php.j2

@@ -233,7 +233,7 @@ $wgFooterIcons = [
 $wgGroupPermissions['maintainer'] = array();
 $wgGroupPermissions['translator'] = array();
 $wgGroupPermissions['archdev'] = array();
-$wgGroupPermissions['archtu'] = array();
+$wgGroupPermissions['archpackager'] = array();
 $wgGroupPermissions['archstaff'] = array();
 $wgGroupPermissions['administrator_fellow'] = array();