Add irc to the allowed URL schemas

I considered adding this to the operations/mediawiki-config, but
why not simply allow irc by default?

Please note that I currently don't want to add mailto by default,
mainly for privacy reasons.

Needs Ib9daa61.

Bug: 72924
Change-Id: I86cff20d3826f90cdbb3086975b5fa8be4a24eac
Merge "Add irc to the allowed URL schemas"