Add semcov for grpc request and response sizes

[anuragagarwal561994]

We are trying to add functionality to yield grpc request and response size metrics.

As I can see it is not part of semcov, how can it be added so we can change the opentelemetry-java instrumentation to yield these metrics?

[breedx-splk]

I think this would fall under this: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/rpc/rpc-metrics.md#metric-rpcserverrequestsize

[anuragagarwal561994]

Yes this is only the metric we wanted to add as attribute so we can extract that attribute in this metric.

[breedx-splk]

Gotcha. I don't think this repo yet has any support for autogenerating the metric conventions from the yaml, so this definitely relates to #12.

[jack-berg]

Closing as duplicate of #12. Keeping #12 instead of this because its more generic, and came first.