upgrade eugeni to bullseye

eugeni is going to be a tricky bullseye upgrade, so it's not part of the large bullseye upgrade batches (#40690 (closed) or #40692 (closed)).

we might want to decide what to do with mailman (#40471) and schleuder (#40564 (closed)) before we do the upgrade. mailman 2, in particular, is EOL so we will need to upgrade or replace it.

we might also want to consider the impact of the %improve mail services roadmap here. it's possible we might want to completely rebuild eugeni in different components instead of upgrading it.

checklist:

• warn about final destruction of (private) archives not migrated to mailman3
• follow eugeni upgrade procedure
• remove mailman2 package, if not done already
• cleanup/remove profile::lists code, take particular care with ssl::service[lists.tpo], see also #41850
• cleanup left private archives, summarizing what was lost