Is your feature request related to a problem? Please describe.
I am instrumenting trace using opentelemetry library in application that uses google cloud resources. Since google cloud library instruments trace using opencensus, I do not see spans for interactions with google cloud resources (e.g. cloud.google.com/go/spanner.ReadWriteTransaction)

Describe the solution you'd like
Trace package to be updated to propagate both opencensus and opentelemetry Span in context and export it to registered Exporter/SpanProcessor

Describe alternatives you've considered
N/A

Additional context
N/A