Allow extra settings for proxies

templates/haproxy_cfg.jinja2

@@ -269,6 +269,9 @@ frontend https_in_{{ cert.ip }}
 {% for external in cert.external|default([]) %}
 
 backend backend_{{ external.key }}
+{% for line in external.extra|default([]) %}
+  {{ line }}
+{% endfor %}
   server server_{{ external.key }} {{ external.server }} check {{ external.options|default('') }}
 {% endfor %}
 {% endfor %}