cloud-trace: Cloud Trace exporter (#698)
cloud-trace: Cloud Trace exporter (#698)

Co-authored-by: Cheng-Lung Sung <d57f5d52a2652fa543edf63007a308e8ede2719c@gmail.com>
open-telemetry/opentelemetry-python-contrib,open-telemetry/opentelemetry-python-contrib,open-telemetry/opentelemetry-python-contrib