The addition of a pp_sortkey field in T60032 necessitates an update
to old entries in the page_props table that don't have a pp_sortkey.
The script uses the pp_value as the sort key if it's numeric.
The script extends LoggedUpdateMaintenance so it only runs once.
Added the script to MysqlUpdater so that it automatically runs.
Bug: T66949
Change-Id: Id482dc73ec1963010324e51fe9273a72dd31a7f7