Two separate implementations of Protobuf serialisation

[jack-burridge-cfh]

There are currently two implementations of Protobuf serialisation in the libraries:

• opentelemetry-exporter-otlp-proto-http
• opentelemetry-exporter-otlp-proto-grpc

Would it make sense to move this serialisation to opentelemetry-proto or another library which these can then both use? This could also be useful for other exporters, for example, publishing spans to Kafka.

The implementation in opentelemetry-exporter-otlp-proto-grpc is not thread safe. I'm unsure if this is a necessity, but given the InMemorySpanExporter uses locks in the export I think it probably is.
The use of the attribute _collector_kwargs to encode the spans and logs is likely to cause an issue if the export is invoked from multiple threads.
Should I raise an issue?

[srikanthccv]

This has come up a few times during reviews and exporter development. The informally agreed upon package was opentelemetry-exporter-otlp-proto-common. I think the opentelemetry-proto should contain the generated code. Happy to help if you are willing to take up the task and send PR.