Exponential Histogram Datatypes

[MadVikingGod]

This patch introduces the Exponential Histogram datatype in the Metrics SDK. This is the serializable format that exporters will use.

This patch does not do the follow, and will this functionality be added in follow on patches:

• Prepare the OTLP exporter to handle this type.
• Create an Aggregator that will export this

EDIT: OTel Spec for reference: https://github.com/open-telemetry/opentelemetry-specification/blob/v1.21.0/specification/metrics/data-model.md#exponentialhistogram

[pellared]

👍

[pellared]

👍

[codecov]

Codecov Report

Merging #4165 (7a36242) into main (844b107) will increase coverage by 0.1%.
The diff coverage is 99.2%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4165     +/-   ##
=======================================
+ Coverage   83.3%   83.4%   +0.1%     
=======================================
  Files        181     181             
  Lines      13986   14116    +130     
=======================================
+ Hits       11657   11786    +129     
- Misses      2102    2103      +1     
  Partials     227     227             

Impacted Files	Coverage Δ
sdk/metric/metricdata/data.go	50.0% <0.0%> (-7.2%)	⬇️
sdk/metric/metricdata/metricdatatest/assertion.go	88.9% <100.0%> (+1.6%)	⬆️
...dk/metric/metricdata/metricdatatest/comparisons.go	90.5% <100.0%> (+2.3%)	⬆️