Prometheus metric endpoint summary metrics do not contain '_sum' field

[Alphayeeeet]

The metrics available under host:port/service/metrics/prometheus are not common to the prometheus format.

For example the following metric does not contain an '_sum' value to be able to calculate the average value by dividing sum/count.

The common format which contains quantiles, sum and count is documented on the official prometheus site: https://prometheus.io/docs/practices/histograms/#count-and-sum-of-observations

Maybe the metric libraries should be updated.

[nblair]

Thanks @Alphayeeeet for opening this; I've labeled it as an Enhancement Request, so we'll leave it open to track demand.