mailman3: IaC list configurations

It is cumbersome to manage the list configurations from the web ui and easy for them to diverge, so let's instead manage them with Ansible.

Fix #254 (closed)

roles/mailman3/defaults/main.yml

@@ -18,6 +18,7 @@ lists:
     subscription_policy: confirm_then_moderate
   arch-devops:
     display_name: Arch-devops
+    description: Arch Linux Infrastructure development discussion
   arch-devops-private:
     advertised: "false"
     archive_policy: private