Request to allow control of which grpc codes set the span to error

[fantapop]

Along the same lines as #1973, we use grpc codes to indicate which errors were caused by a users action. Currently any error that's passed back through the grpc interceptor is setting the span to error. This makes it more difficult to see which errors are actionable in our request dashboards. I have some local changes that allows passing a function in as configuration which would determine whether an error should set the span status to code. Is this something you'd accept a PR for?

I'm currently doing this but happy to do it differently or change the names of variables etc, thanks.

		if err != nil {
			s, _ := status.FromError(err)
			if config.SpanErrorClassifier(err) {
				span.SetStatus(codes.Error, s.Message())
			}
			span.SetAttributes(statusCodeAttr(s.Code()))
			messageSent.Event(ctx, 1, s.Proto())
		} else {
			span.SetAttributes(statusCodeAttr(grpc_codes.OK))
			messageSent.Event(ctx, 1, resp)
		}

[MrAlias]

Please take a look at open-telemetry/opentelemetry-specification#3110. We need to specification to evolve before we can change this instrumentation to deviate.