1.0 release opentelemetry-proto

[cijothomas]

https://github.com/open-telemetry/opentelemetry-rust/blob/main/opentelemetry-proto/Cargo.toml

This crate is used more widely than a mere internal dependency for the OTLP Exporter crate.

Opening an issue to track getting this to 1.0 stable. The protos themselves were declared stable, so this should be relatively easy.