T203529: Set up a packagist mirror for Wikimedia / https://packagist-mirror.wmcloud.org/

The idea was to be more resilient and independent plus get some better performance by running our own packagist mirror, potentially even in production.

The set up is pretty simple, it's a git checkout of https://github.com/Webysther/packagist-mirror with some apache config and a systemd timer.

Based on access logs, some people are using it. It needs some love, like migrating to Buster or Bullseye (T277250) and switching to the new, official, mirror scripts: https://github.com/composer/mirror

I'm not really interested in running it any more, upstream packagist is pretty stable these days, and it's actually an open source project (unlike npmjs.com) so I don't ideologically feel bad about using it. If someone else wants to run this, happy to hand it over. Otherwise I'll sunset it.