Setup mailman3 server

We want to migrate to mailman3 as mailman2 is basically unmaintained and requires Python 2 which is EOL.

Because the mailman and mailman3 packages conflict and we don't want to perform a big bang migration, mailman3 must be deployed on a separate server. mailman-web (mailman3's web interface) hasn't been packaged yet, so for now we are using my homebrewed PKGBUILD.

[1] https://gist.github.com/klausenbusk/5982063f95c503754a51ed2fefb8915e

Ref #59 (closed)

---

Migrated lists:

• arch-announce
• arch-devops-private
• arch-events
• arch-wiki-admins

roles/mailman/templates/main.cf.j2

@@ -22,7 +22,7 @@ mynetworks =
     127.0.0.0/8
     [::1]/128
     [fe80::]/64
-     {{ hostvars['mailman3.archlinux.org']['wireguard_address'] }}
+    {{ hostvars['mailman3.archlinux.org']['wireguard_address'] }}
 
 # fatal: configuration error: mailbox_size_limit is smaller than message_size_limit
 message_size_limit = 104857600