Support interpolation of rule variables into conditionalFhirPathExpression

[LZRS]

Describe the feature request.
Support passing of computed rule variables as part of the fhirpath expression used in conditionalFhirPathExpression

Additional context
In the wdf project, a usecase came up where we needed to show a list of medications filter by the latest date of encounter. This feature would assist in passing the latest medication date as part of the conditionalFhirPathExpression

  {
                  "id": "availableMedication",
                  "relatedResourceId": "availableMedicationRequest",
                  "resourceType": "MedicationRequest",
                  "conditionalFhirPathExpression": "MedicationRequest.id.toString().contains('@{latestMedicationDateSimpleFormat}')",
        }