Zone aware routing

[dsvetl]

Hi, projectcontour,

You need to add the ability to contour to use this functionality in envoy

https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/upstream/load_balancing/zone_aware#arch-overview-load-balancing-zone-aware-routing

I wish we can parse pod region/zone to provide this info into xDS API.