Proposal: Istio Config Metrics

Doc link: http://tinyurl.com/y584vxq7

I believe that Istio would benefit from exposing metrics around the configuration state of the system. I believe that it would allow correlating config changes with observed behavioral changes, as well overall making the system easier to troubleshoot and debug (without having to be a kubectl expert).

Would very much appreciate community feedback.

Thanks for listening,
Doug.

cc: @ozevren @ayj @gargnupur