(Bug 45607) Add a callback for the hook for reordering of special pages

This callback is for the hook in https://gerrit.wikimedia.org/r/#/c/51827/

Change-Id: Iab2536c894c350f77e1619315fd8f55a7a1db5ac
Merge "(Bug 45607) Add a callback for the hook for reordering of special pages"