Add Consent Check Implementation

[hhund]

The transfer process should check, if a valid consent resource is available for the patient whose data is to be transported. A ConsentClient needs to be implemented and the ConsentClientFactory needs to be modified.

Two implementations of ConsentClient should be available:

Priority 1: FHIR Client searching for Consent resources at the local GECCO FHIR server.
Priority 2: FHIR Client searching for Consent resources at the local gICS server.