Add origin response time and keycdn response time in logs


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.