OpenTelemetry Exporter integration with Resource API

[hectorhdzg]

Resource API need to be integrated with exporter code to allow customers to configure cloud extension data like roleName, roleInstance among others
https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable

[lzchen]

On a related note, the attributes within a Resource should also be exported for each envelope in the Azure exporters.