Create php-fpm pool for MediaWiki SaaS

Summary:
Allow to create a php-fpm pool, without taking care of the user account.

Environment contains public settings, but not private ones.

wikis.nasqueron.org is a virtual, not currently existing domain,
for php-fpm configuration purpose.

Ref T845.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T845

Differential Revision: https://devcentral.nasqueron.org/D1446