Add mailcow to terraform

templates/infrastructure.d2.j2

@@ -74,6 +74,13 @@ external: {
 external.scaleway.s3.{{ svc.name }}
 {% endif %}
 
+{% if svc.mail %}
+{{ svc.key }} -> {{ mail_key }}: {
+    style.stroke: "#C9B81F"
+}
+{{ mail_key }}.{{ svc.name }}
+{% endif %}
+
 {% endfor %}{# svc #}
 
 {% for svc in grid_svcs %}