Add a dynamic Webmail option with a 'none' container

.env

@@ -25,6 +25,9 @@ HOSTNAME=mail.freeposte.io
 # Postmaster local part (will append the main mail domain)
 POSTMASTER=admin
 
+# Choose which webmail to run if any (values: roundcube, none)
+WEBMAIL=none
+
 # Networks granted relay permissions, make sure that you include your Docker
 # internal network (default to 172.17.0.0/16)
 RELAYNETS=172.16.0.0/12