Should we improve error handling when patient reference is not relative?

[Reinaard]

When patient reference is not a relative url, then we get an error: Reference is not a valid Patient reference. Maybe it's a good idea to give a more specific error message like Patient reference can only be relative?

To Reproduce

Steps to reproduce the behavior:

1. Register a bundle ar /registration

{
    "resourceType": "Bundle",
    "type": "transaction",
    "id": "bundle-careplan-example-012",
    "entry": [
        {
            "fullUrl": "https://patientendossier.nl/Patient/patient-018",
            "resource": {
                "resourceType": "Patient",
                "id": "patient-018",
                "identifier": [
                    {
                        "system": "http://fhir.nl/fhir/NamingSystem/bsn",
                        "value": "482169084"
                    }
                ],
                "name": [
                    {
                        "use": "official",
                        "family": "Jones",
                        "given": [
                            "Rita"
                        ]
                    }
                ],
                "gender": "male",
                "birthDate": "2000-01-31"
            },
            "request": {
                "method": "POST",
                "url": "https://patientendossier.nl/Patient/patient-018"
            }
        },
        {
            "resource": {
                "resourceType": "Immunization",
                "id": "imm123",
                "status": "completed",
                "vaccineCode": { "text": "Influenza vaccine" },
                "patient": { "reference": "https://patientendossier.nl/Patient/patient-018" },
                "occurrenceDateTime": "2024-11-15"
            }
        }
    ]
}