Add support for Exponential Histograms

[pichlermarc]

Implement the Exponential Histogram Aggregation based on the specificiation.

This is an (most likely incomplete) list of things that need to be implemented for this feature:

• implement an Aggregator
• implement an Accumulation
• create a representation that will be sent to the exporter via toMetricPoint() on the Aggregator that will be eventually passed to the metric exporters
• add an static ExponentialBucketHistogramAggregation() method to the Aggregation class and implement the Aggregation modeled after the HistogramAggregation
• add an Interface for the Exponential Histogram to the @opentelemetry/otlp-transformer package's types, so that it can be transformed to the OTLP representation (and subsequently serialized to proto or json and exported)

[dyladan]

I started on a prototype for this but it is not production ready by any means. If someone wants to work on this you can reach out to me and I can share what I have, otherwise I'll work on this after the metrics release.

[mwear]

I'll take this if it's still up for grabs.

[github-actions]

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