TPA-RFC-44: Email emergency recovery

To respond to the bouncing email crisis (tpo/web/civicrm#74), I've drafted a new proposal to implement emergency measures but also a long term plan to host our own email properly:

https://gitlab.torproject.org/tpo/tpa/team/-/wikis/policy/tpa-rfc-44-email-emergency-recovery

This ticket provides a space to review the proposal, express dissent, encouragement, or any other comments.

next steps:

2. make tickets for the work to be done in emergency
3. update the status page (https://status.torproject.org/issues/2022-11-30-mail-delivery/)
4. SPF (hard), DKIM and DMARC (soft) records on CiviCRM (#40986 (closed))
5. DKIM signatures on eugeni and submission (#40988 (closed))
6. DKIM signature on all mail hosts (#40989 (closed))
7. Deploy SPF (hard), DKIM, and DMARC records for all of torproject.org (#40990 (closed))
8. Deploy a new, sender-rewriting, mail exchanger (#40987) postponed to next year, followup in #41009
9. update the status page (https://status.torproject.org/issues/2022-11-30-mail-delivery/)
10. update the documentation in howto/submission and service/email.md
11. split long-term parts of TPA-RFC-44 out of it into a new proposal (yes, editing the standard, omg) followup in #41009