Proposal: Move opentelemetry-semantic-conventions to opentelemetry-rust-contrib

[cijothomas]

This repo should hold crates that implement the OTel spec. Semantic conventions are not part of the spec — they live in their own repo with their own release cadence — and their primary consumers are instrumentation libraries, which we host in opentelemetry-rust-contrib. Other SIGs already separate this: .NET ships semantic conventions from opentelemetry-dotnet-contrib, Java from a dedicated repo.

Proposing we move opentelemetry-semantic-conventions to opentelemetry-rust-contrib. Filing this to start a SIG discussion.

[scottgerring]

This sounds sensible to me 👍