feat(nginx): Route /mxdeliv/ to configurable port (#901)

cmdeploy/src/cmdeploy/nginx/nginx.conf.j2

@@ -73,6 +73,10 @@ http {
 
 		access_log syslog:server=unix:/dev/log,facility=local7;
 
+		location /mxdeliv/ {
+		    proxy_pass http://127.0.0.1:{{ config.filtermail_http_port }};
+		}
+
 		location / {
 			# First attempt to serve request as file, then
 			# as directory, then fall back to displaying a 404.