Add Backend method to retrieve data actually submitted

[cqc-alec]

Given the handle returned by process_circuits(). This would mean maintaining a cache of these, as we do for results.

The return type would vary from backend to backend (QASM, QIR, qiskit circuit, ...), so we'd probably also want to add a property for that.

[github-actions]

This issue has been automatically marked as stale.