set ip to bind in reverse proxy http configuration

Because we are using openwrt and we would like to mantain LUCI running
on it's interface we can't bind on 0.0.0.0. or 127.0.0.1 hence we must
listen on a specific ip. This will set the public ip from the group
vars to be the one where we listen

group_vars/all.yaml.example

@@ -3,3 +3,5 @@
 ext_gateway: ""
 # Put here the public key of the users CA.
 user_ca_key: ""
+# Put here the public ip for your organisation
+public_ip: 0.0.0.0

roles/reverse_proxy/templates/http.j2

@@ -1,5 +1,5 @@
 server {
-    listen 80;
+    listen {{ public_ip }}:80;
 
     server_name {{ hostname }}.lilik.it www.{{ hostname }}.lilik.it;