stackdriver: update gRPC schemas

[djc]

No description provided.

[cijothomas]

@djc For my own learning purposes: Is the StackDriver package crate actively maintained? I see that JavaScript SIG deprecated it long ago :https://www.npmjs.com/package/@opentelemetry/exporter-stackdriver-trace

The .NET one has a note saying its not maintained by Google : https://github.com/open-telemetry/opentelemetry-dotnet-contrib/tree/main/src/OpenTelemetry.Exporter.Stackdriver#stackdriver-exporter-for-opentelemetry-net

Google's own doc suggests to use Zipkin exporter
https://cloud.google.com/trace/docs/setup#how_to_instrument_applications
https://cloud.google.com/trace/docs/zipkin

[djc]

Yes, I'm maintaining this crate. It is still named -stackdriver for continuity, but under the hood it uses the gRPC API for Cloud Trace, so that seems to be the preferred path per Google's documentation.