Provide configuration for wikis

Summary:
Prepare the MediaWiki configuration for every wiki of the farm.

This service responsibility is to resolve host to a specific database
and set of configuration and populate the relevant MediaWiki configuration.

This acts as the SaaS MediaWiki entry point.

Ref T845

Test Plan:

• Ensure $wgConf is coherent
• Check we've a wiki up in root URL scheme (agora)
• Check we've a wiki up in wiki URL scheme (wolfplex)

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T845

Differential Revision: https://devcentral.nasqueron.org/D1442