Enable Extension:NewUserMessage on ukwiki

This patch enables the NewUserMessage extension on
the Ukrainian Wikipedia per community request.

Newly registered users as well as global users with
autocreated accounts (through CentralAuth) will
receive welcome messages on their talk pages.

See bug for URL with on-wiki consensus.

Bug: 65125
Change-Id: I1d54bfedd98616a6d9a1092f488f243df8f237e6