roles/archwiki: Added the path to the php-fpm path

Define the path as a variable for usage on the php-fpm configuration.

roles/archwiki/defaults/main.yml

@@ -2,6 +2,7 @@
 archwiki_dir: '/srv/http/archwiki'
 archwiki_domain: 'wiki.archlinux.org'
 archwiki_user: 'archwiki'
+archwiki_socket: '/run/php-fpm/archwiki.socket'
 
 archwiki_db: 'archwiki'
 archwiki_db_host: 'localhost'