Support Gauge Distributions in Cloud Monitoring Exporter

[ItsLastDay]

My team is maintaining an OTel collector. We provide this collector to other teams at Google. Those teams use the collector to gather metrics about their VMs/clusters/... .

One of our customers has a Gauge Distribution metric in Cloud Monitoring. It is a valid thing, according to https://cloud.google.com/monitoring/api/v3/kinds-and-types#kind-type-combos.

However, in OTel, only Delta and Cumulative histograms (distributions) exist. Thus, there is no way to express gauge distributions. We would like to have this functionality.

[damemi]

We are probably planning this eventually, but right now we want to target #624 first

[dashpole]

I think this would require OTel spec changes. At minimum, it would need to be added to the OTel data model.