Merge branch 'mail_dnssec' into 'master'

mail: enable dnssec for static-mail-domains

See merge request !38

roles/mail/templates/dns/static-mail-domains.yml

 {% for domain in static_mail_domains %}
 {{ domain }}:
+  DNSSEC: "true"
   EXTENDS: ["@base", "@hosted_mail_mixin"]
 
 {% endfor %}