[histograms] try out DDSketch

[okayzed]

Seems like it might be quite fast and accurate, as well as mergeable. This task is to try it out https://github.com/DataDog/sketches-go

[okayzed]

need to add support for weighted values to the sketch, but preliminary timings show that the DDSketch is not much slower than the default naive histogram.

accuracy at the min value and max value was within 0.5% of the naive histogram