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)

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Migrated lists:

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

playbooks/mailman3.archlinux.org.yml

+- name: setup mailman3 server
+  hosts: mailman3.archlinux.org
+  remote_user: root
+  roles:
+    - { role: common }
+    - { role: firewalld }
+    - { role: wireguard }
+    - { role: sshd }
+    - { role: root_ssh }
+    - { role: hardening }
+    - { role: borg_client, tags: ["borg"] }
+    - { role: prometheus_exporters }
+    - { role: promtail }
+    - { role: nginx, nginx_firewall_zone: wireguard }
+    - { role: uwsgi }
+    - { role: postgres }
+    - { role: mailman3 }