Support for Gauge Distribution

[huyan0]

Is your feature request related to a problem? Please describe.
Hello, I am new to OpenCensus and Observability, and this is more of a question than feature request. I am working on Prometheus remote write API exporter for the OpenTelemetry collector project and using this repository as reference.

I noticed that Gauge Distribution is not supported here. Is there a specific reason? How is that different from cumulative distribution? I looked at how Prometheus histogram type is different from distribution but wasn't able to figure it out. The only difference between gauge and counter distribution seems to be whether sum and count can go down or not, and this shouldn't matter in the context of exporting to Prometheus.

Additional context
OpenTelemtry's Prometheus exporter uses orijtech's exporter, is this project a re-implementation of that?