postfix: allow to override mailname

postfix/defaults/main.yml

@@ -3,6 +3,7 @@
 postfix_domains:
   - "{{ domain }}"
 postfix_virtual_domains: []
+postfix_mailname: "{{ domain }}"
 
 postfix_tls_cert: /etc/ssl/private/fullchain.pem
 postfix_tls_key: /etc/ssl/private/privkey.pem

postfix/templates/mailname.j2

-{{ domain }}
+{{ postfix_mailname }}