DataPower OpenTelemetry: export spans for every transaction while propagating the incoming parent's sampled flag unchanged to the backend

We run DataPower as the API Gateway in API Connect and export gateway spans via OpenTelemetry to our own collector. The collector derives metrics from all spans (request count, latency, errors per API) and then forwards only the traces our central tracing platform should keep. 

For this, the gateway needs to treat two decisions separately:

1. Local recording: should the gateway create and export spans for this transaction?
2. Propagation: which sampled flag goes to the backend in the outgoing `traceparent`?

Today both are tied to one sampler. With `parent-based on`, an incoming `traceparent` with sampled flag `00` means the gateway records nothing, so we lose these transactions for metrics and error analysis. With `parent-based off` and `ratio 100`, the gateway records everything, but it also changes the outgoing flag from `00` to `01`. The backend and every downstream service then start sampling requests the calling application had explicitly decided not to sample. That overrides the caller's decision and multiplies trace volume downstream.

What we would like:

- A sampler or propagation option that records and exports spans for every transaction, regardless of the incoming parent.
- The outgoing `traceparent` keeps the sampled flag of the incoming parent. If there is no valid incoming parent, the gateway acts as root and sends `01` (or follows the configured root sampler).
- The incoming parent's sampled decision as a span attribute on the server span (for example `datapower.parent.sampled=true|false`, name up to IBM), so a collector can filter the trace branch afterwards. OTLP does not carry the parent's sampled flag, so the collector cannot reconstruct it today.

This helps every platform team that uses gateway spans for analysis and debugging and needs to take into account the sampling decisions made by the calling applications so as not to overload the entire underlying backend network with all the traces.