WIP: new check-advisories command
This command makes sure that all advisories in the security tracker are regularly published on the website.
It can be called in DSA or DLA mode and will (respectively) check for official security advisories or LTS advsiories on a local copy of the website.
It does not check the integrity of that copy, it only checks to see if it's there.
This is useful to make sure we don't forget to publish some advisories.
This is a replacement for webwml!52 (closed)