Deploy MediaWiki SaaS on Alkane PaaS

Summary:
MediaWiki will run on web-001 as a first test of Alkane capabilities.

Database is served from db-B-001.

Improve interaction between saas-mediawiki and webserver-alkane,
and allow a smotoh installation or highstate, first of the PaaS
layer, then the SaaS layer.

Ref T1803

Test Plan: Deploy on web-001

Reviewers: dereckson

Maniphest Tasks: T1803

Differential Revision: https://devcentral.nasqueron.org/D3049