metrics: implement Sketch aggregator

[vmarchaud]

Spec: https://github.com/jmacd/opentelemetry-specification/blob/jmacd/draft_metric_sdk_spec/specification/sdk-metric.md#L242

Go impl: https://github.com/open-telemetry/opentelemetry-go/blob/master/sdk/metric/aggregator/ddsketch/ddsketch.go

The go implementation use https://github.com/DataDog/sketches-go to do the actual math, sadly no implementation exists currently in JS or TS so we'll need to write one

[vmarchaud]

The spec has been updated to list different algorithm that we can use for this:

Example algorithms that could be used to implement this aggregator are include: GK-Sketch, DDSketch, Q-Digest, T-Digest, and HDR-Histogram

Fortunaly, HDR-Histogram have a pure typescript implementation available there https://github.com/HdrHistogram/HdrHistogramJS so we can use that

[vmarchaud]

I don't have much time to work on this so i prefer to de-assign myself. However from the initial work i've done, extracting the code from the library i've mentionned above is quite complex so i would in favor to add it as a dependency. Another solution is to re-write any of the above algorithms

[legendecas]

Closing as the feature has been removed in the spec.