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/nginx.d.conf.j2

@@ -52,7 +52,7 @@ server {
 
     location ~ ^/(static|mailman3|archives|accounts|admin3)($|/) {
         proxy_pass http://{{ hostvars['mailman3.archlinux.org']['wireguard_address'] }};
-        proxy_set_header Host lists.archlinux.org;
+        proxy_set_header Host {{ lists_domain }};
         proxy_set_header X-Forwarded-For $remote_addr;
     }