Verify DSC behavior

[elramen]

Verify that the following happens in both the v2 and transactions pipelines:

• DSC is Some and same trace-origin org:
  • sampling_project_info (and thereby root project id) must be Some
  • do not fall back to current transaction if missing
• DSC is Some and different trace-origin org:
  • sampling_project_info (and thereby root project id) must be None
  • Infer project id, transaction and the rest of the dsc (using current transaction)
• DSC is None and transaction/otel span:
  • DSC and project id are not inferred.
  • 100% SR.
• DSC is None and v2 span (that doesn't come from otel):
  • Reject the span.

[linear-code]

RELAY-250