Add origin response time and keycdn response time in logs


#1

The current log format of KeyCDN doesn’t return any details on the response time of the origin and on the response time of KeyCDN.

origin response time : nginx variable $upstream_response_time
keycdn response time : nginx variable $request_time

I think that we don’t care of the origin shield intermediate response time.

For instance, this is very important to troubleshoot issues on Googlebot reporting high response time.