TPA-RFC-57: bookworm upgrade plan

in the %Debian 11 bullseye upgrade we did three main batches of upgrades, and that worked extremely well.

do something similar to https://gitlab.torproject.org/tpo/tpa/team/-/wikis/policy/tpa-rfc-20-bullseye-upgrades but take into account the bullseye post-mortem. specifically, don't block the upgrade on complex services, if at all possible.

also need to consider the trailing %Debian 11 bullseye upgrade servers (6 at the current count), although those are mostly going to be rebuilt (pauli/eugeni/nagios) or retired (cupani, vineale). The only one that still needs a kick is alberti, and it's possible it could be double-upgraded to bookworm as well.

this is being drafted in https://gitlab.torproject.org/tpo/tpa/team/-/wikis/policy/tpa-rfc-57-bookworm-upgrades