Expose $request_time as X-Server-Proxy-Time response header

Author: itskingori

config/http.conf

@@ -77,6 +77,7 @@ http {
   proxy_set_header    X-Forwarded-Port    $proxy_x_forwarded_port;
   proxy_set_header    X-Request-ID        $proxy_x_request_id;
   proxy_set_header    X-Forwarded-Host    $proxy_x_forwarded_host;
+  proxy_set_header    X-Server-Proxy-Time $request_time;
 
   gzip on;
   gzip_comp_level 5;