Need example of how to build a histogram with exponential bucket boundaries

[breedx-splk]

This came up in slack. There are currently no examples here of how to create a histogram with exponential bucket boundaries. A user reading the example for Histogram today might believe that it's simply missing from the implementation.

As a result, I think it probably makes sense to add an example for exponential buckets to the existing example. That way, it's pretty easily findable (just like the custom bucket example is findable).

[jaydeluca]

I took a stab at this (#396 )

I assume the approach I took will be a more useful example than just demonstrating the use of the system property/env var otel.exporter.otlp.metrics.default.histogram.aggregation and OTEL_EXPORTER_OTLP_METRICS_DEFAULT_HISTOGRAM_AGGREGATION, to enable it, but let me know if you had something else in mind.