Propagate tracing context headers

Some SAPI endpoints might return tracing context headers (like `traceparent` and `traceparent`, see W3C [Trace Context](https://www.w3.org/TR/trace-context/)), so it's desirable to propagate that context to relevant subsequent requests.

For example:
- context received on job submission should be propagated in job status poll and answer download requests
- context received on problem data upload should be propagated in job submission requests