Contribute otel-arrow-rust to OTEL

[v0y4g3r]

otel-arrow-rust is a Rust implementation of otel-arrow protocol. This implementation currently supports the univariate metrics signal. This contribution is considered a useful starting point for a complete Rust implementation of OTAP.

Part of #294
Part of open-telemetry/opentelemetry.io#6410

Originally authored at https://github.com/v0y4g3r/otel-arrow-rust

[jmacd]

I reviewed this code in depth. I am a big fan, thank you @v0y4g3r.

As a relatively new Rust programmer, this gives me a substantial boost in productivity. I would be able to add support for the other signal types by following the example here for metrics.

Further, I am interested in benchmarking OTAP-to-OTLP (and later OTLP-to-OTAP) conversion functions; this will provide a valuable reference implementation. I believe as part of #294 our goal should be to optimize the OTAP-to-OTLP-bytes function directly--I'd like to experiment with encoding protobuf bytes directly from OTAP (i.e., w/o an intermediate prost::Message) and I would like to use this library as a starting point.

As I said for the Beaubourg contribution, #293 (review), there will be some degree of style differences in the repository in the short term, but nothing we can't fix as the project progresses.