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/mailman3/templates/settings.py.j2

@@ -14,10 +14,9 @@ ADMINS = (
 DATABASES = {
     'default': {
         'ENGINE': 'django.db.backends.postgresql_psycopg2',
-        'NAME': 'malman-web',
+        'NAME': 'mailman-web',
         'USER': '{{ vault_mailman_web_db_user }}',
         'PASSWORD': '{{ vault_mailman_web_db_password }}',
-        'HOST': '127.0.0.1',
     }
 }