Native histogram support

[jmcarp]

This is a question and possibly a feature request: does promxy support prometheus native histograms? Would we need to update the vendored prometheus fork for this to work?

[jacksontj]

Short answer, yes.

Longer answer: Histograms are actually more-or-less calculated query side (https://prometheus.io/docs/prometheus/latest/querying/functions/#histogram_quantile). So this (under the hood) is the same as all of the other servergroup merging.

[jmcarp]

Thanks!