Update AccessDelegation model to latest API ontology

According to the API spec, AccessDelegation's property hasDescription is an optional xsd:string

Current implementation in AccessDelegation model parses this property into a Set. see https://git.openlogisticsfoundation.org/wg-digitalaircargo/ne-one/-/blob/da53bb366434dfe572a04bbc247da0eb577ec4c9/src/main/java/org/openlogisticsfoundation/neone/model/AccessDelegation.java#L21

In addition, the conversion from String to Set seems to lead to incorrect results.

The following AccessDelegation

{
    "@context": {
        "cargo": "https://onerecord.iata.org/ns/cargo#",
        "api": "https://onerecord.iata.org/ns/api#"
    },
    "@type": "api:AccessDelegation",
    "api:hasDescription": "Require access to Piece for handling",
    "api:hasPermission": [{
            "@id": "api:GET_LOGISTICS_OBJECT"
        }
    ],
    "api:isRequestedFor": [{
        "@id": "http://www.w3.org/ns/auth/acl#AuthenticatedAgent"
    },
    {
        "@id": "http://localhost:8080/logistics-objects/_data-holder"
    }],
    "api:notifyRequestStatusChange": false,
    "api:hasLogisticsObject": [{
        "@id": "http://localhost:8080/logistics-objects/a50d0a65-c0ec-4183-be4e-bac3fec4023a"
    }]
}   

leads to

{
    "@graph": [
        {
            "@id": "http://localhost:8080/action-requests/73452e6c-bb60-4a38-bf90-bd9fe3a32f2b",
            "@type": "https://onerecord.iata.org/ns/api#AccessDelegationRequest",
            "https://onerecord.iata.org/ns/api#hasAccessDelegation": {
                "@id": "neone:b8a4eb3c-a12a-4bfb-a3fa-e58d3a7fc2de"
            },
            "https://onerecord.iata.org/ns/api#hasRequestStatus": {
                "@id": "https://onerecord.iata.org/ns/api#REQUEST_ACCEPTED"
            },
            "https://onerecord.iata.org/ns/api#isRequestedAt": {
                "@type": "xsd:dateTime",
                "@value": "2023-11-08T16:03:06.804947Z"
            },
            "https://onerecord.iata.org/ns/api#isRequestedBy": {
                "@id": "http://localhost:8080/logistics-objects/_data-holder"
            }
        },
        {
            "@id": "neone:b8a4eb3c-a12a-4bfb-a3fa-e58d3a7fc2de",
            "@type": "https://onerecord.iata.org/ns/api#AccessDelegation",
            "https://onerecord.iata.org/ns/api#hasDescription": "[[Require access to Piece for handling]]",
            "https://onerecord.iata.org/ns/api#hasLogisticsObject": {
                "@id": "http://localhost:8080/logistics-objects/a50d0a65-c0ec-4183-be4e-bac3fec4023a"
            },
            "https://onerecord.iata.org/ns/api#hasPermission": {
                "@id": "https://onerecord.iata.org/ns/api#GET_LOGISTICS_OBJECT"
            },
            "https://onerecord.iata.org/ns/api#isRequestedFor": {
                "@id": "http://www.w3.org/ns/auth/acl#AuthenticatedAgent"
            },
            "https://onerecord.iata.org/ns/api#notifyRequestStatusChange": {
                "@type": "xsd:boolean",
                "@value": "false"
            }
        }
    ],
    "@context": {
        "xsd": "http://www.w3.org/2001/XMLSchema#"
    }
}