[Wiki] Convert backend from Postgre to MariaDB

[broxen]

Summary

It appears that Postgre support in MediaWiki is sketchy at best. Let's just move to MariaDB and make our lives easy.

The simplest path is to export existing work (we don't need History or User Pages), using the maintenance scripts located in /wiki/maintenance/, then import using the scripts there as well.

Let's ensure that we get all Files/Media/Images in the move.

References

https://www.mediawiki.org/wiki/Manual:Moving_a_wiki
https://www.mediawiki.org/wiki/Help:Export
https://meta.wikimedia.org/wiki/Help:Import

[broxen]

Targeting this weekend: May 4-5 to complete this.