feat: add mail::gateway role

- add a mail::gateway role, more to add later
- enables the build of hosts in this role immedately (config later)

site/roles/manifests/infra/mail/gateway.pp

@@ -0,0 +1,10 @@
+# a role to deploy a dmz mx gateway for mail services
+class roles::infra::mail::gateway {
+  if $facts['firstrun'] {
+    include profiles::defaults
+    include profiles::firstrun::init
+  }else{
+    include profiles::defaults
+    include profiles::base
+  }
+}