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/files/transport

+# AUTOMATICALLY GENERATED BY MAILMAN ON 2021-07-03 22:52:50
+#
+# This file is generated by Mailman, and is kept in sync with the binary hash
+# file.  YOU SHOULD NOT MANUALLY EDIT THIS FILE unless you know what you're
+# doing, and can keep the two files properly in sync.  If you screw it up,
+# you're on your own.
+    
+# Aliases which are visible only in the @lists.archlinux.org domain.
+test@lists.archlinux.org                        lmtp:[10.0.0.2]:8024
+test-bounces@lists.archlinux.org                lmtp:[10.0.0.2]:8024
+test-confirm@lists.archlinux.org                lmtp:[10.0.0.2]:8024
+test-join@lists.archlinux.org                   lmtp:[10.0.0.2]:8024
+test-leave@lists.archlinux.org                  lmtp:[10.0.0.2]:8024
+test-owner@lists.archlinux.org                  lmtp:[10.0.0.2]:8024
+test-request@lists.archlinux.org                lmtp:[10.0.0.2]:8024
+test-subscribe@lists.archlinux.org              lmtp:[10.0.0.2]:8024
+test-unsubscribe@lists.archlinux.org            lmtp:[10.0.0.2]:8024