audit servers for compatibility with buster-lts

it seems likely that we'll miss the target date for the bullseye EOL for all the machines. we still have a handful of boxes that were not upgraded to bullseye still (13, or ~13%), and it's unlikely they will be upgraded before the planned EOL date (august 1st, according to the Debian/LTS page).

Thankfully, we don't need a sources.list change, from what I understand. But the scope of supported packages is different in LTS than in regular debian. So that should be audited. According to the using page, we are supposed to install the debian-security-support package and run check-support-status on those machines.

It might actually be worth doing everywhere too, but that's not within the scope of this ticket (unless it's easier to just do everywhere of course).

Based on the result of those checks, we might want to expedite upgrades on certain machines as well.