Add interwiki agora: and wolfplex:

Summary:
Create a more restricted user for MediaWiki maintenance.
Privileges are limited to the affected tables.

Populate a support SQL script with the interwiki list.
The use of REPLACE allows to avoid to read tables first;
the script is safe to run each time it's modified.

Install MariaDB client on saas-mediawiki role,
so that script can be run from there.

References:

• https://www.mediawiki.org/wiki/Manual:Interwiki
• https://www.mediawiki.org/wiki/Manual:Interwiki_table

Test Plan:

• Create a link [[agora:Operations grimoire]] on Wolfplex wiki

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3736