Add support for exponential histograms

[tgwizard]

Fix for #357. Based on the Go / TS implementations, https://github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/d6795b491c748855e4a4d6eec07ae2cb44a78da1/exporter/metric/metric.go#L723.

I've tested this on a small app, and it seems to work fine.

[google-cla]

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[dashpole]

/gcbrun

[tgwizard]

@dashpole I see the linting errors (I had a hard time getting my IDE to respect the settings). I've now pushed a fix manually.

[dashpole]

/gcbrun

[tgwizard]

@dashpole most of CI seems to pass, I'm not sure how to parse the e2e test failures, if they are related to this PR.

[tgwizard]

Gentle bump on this @dashpole @aabmass

[aabmass]

LGTM, please just address @DylanRussell's comment

[aabmass]

Thank you for the PR!

[tgwizard]

Fix pushed, thank you @DylanRussell @aabmass

[DylanRussell]

/gcbrun