The new metric SDK should support exponential histograms.

This would require a way to select them as an aggregation, and the data type in the export path.

The plan as it currently stands is:

• Support Exponential Histograms in metricdata package (Exponential Histogram Datatypes #4165)
• Support Exponential Histograms in exporters (Add Exponetial Histograms to otlp transforms #4222)
• Create an Exponential Histograms internal.Aggregation(Add the Exponential Histogram Aggregator. #4245)