Is your feature request related to a problem? If so, please describe it.

today the metrics name are too verbose. they either contain "custom.googleapis.com/", or "OpenCensus" (without the ability to add to that prefix).
that makes it harder to use in stackdriver, as the actual metric name is not in the display in the picker.

Describe the solution you'd like.

I would like to be able to define in the StackdriverStatsConfiguration a display name, and this will be used in CreateMetricDescriptorExporter#CreateMetricDescriptorExporter (or directly in StackdriverExportUtils#getDisplayNamePrefix)

Describe alternatives you've considered.

none come to mind