Opt-in items and bytes counts at the node level.

[jmacd]

Pre-filing checklist

• I searched existing issues and didn't find a duplicate

Component(s)

Rust OTAP dataflow (rust/otap-dataflow/)

Description

We have node-level metrics for requests consumed and produced following OTel Collector semantic conventions.

We also want item counters and bytes counters of the same form.

Additional Context

https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/rfcs/component-universal-telemetry.md defines otelcol.{component_type}.produced.items for example.

We should support an opt-in metric for bytes and items.

Note that it may be possible to compute num_items and num_bytes once per (Context, Payload), if done carefully, so that we only recompute the number of items once per request (/mutation) in the pipeline. However, this is not a requirement.

[drewrelmas]

I don't necessarily see this as conflicting with the work in #2859, they target two separate things:

1. Per-component signal counts (parity with Collector metrics)
2. Per-flow signal counts (Operator-defined logical groups)