Add Istio to the Prometheus metrics library
We should add Istio generated metrics to the built-in metrics library of GitLab. Note that this will likely require special handling, since we would want to uniquely identify the services rather than sum them all together in most cases.
- Display response metrics for inbound user requests, like we do today for nginx-ingress. This should allow us to still provide metrics like latency and throughput when Istio is used in place of nginx-ingress.
- Summary information: # of microservices, etc.
- Add a new service section, which isolates each of the services that Istio has metrics for into their own set of response metrics. This would provide service specific metrics for things like error rate, latency, etc.