Migrate the wiki to keycloak

In the future we want to use keycloak for authentication mediawiki:

• https://www.mediawiki.org/wiki/Extension:OpenID_Connect
• https://stackoverflow.com/questions/16893589/prevent-users-from-changing-their-passwords-in-mediawiki
• https://wiki.archlinux.org/index.php/ArchWiki:Access_levels_and_roles

/cc @pierre @archlinux/teams/wiki/admins