Check incoming traces with isRemote and implement logic

Handle spans that have `isRemote` set to `True`. 

* **span processor** (potel_span_processor.py)
  Also check for `isRemote` when assembling the transaction to be sent to Sentry.
* **propagator**
  In the `extract` method: create new OTel context with a virtual remote span set as the active span containing the data of the incoming trace information.