Update Subscription model to latest API ontology

The current specification of the Subscription model expects an optional https://onerecord.iata.org/ns/api#hasDescription property. See https://iata-cargo.github.io/ONE-Record/subscriptions/#publish-subscribe-in-one-record

The current implementation of Subscription model in ne-one server does not include this property. see https://git.openlogisticsfoundation.org/wg-digitalaircargo/ne-one/-/blob/fb88aa7eeaf028802d99c3bc028807d66b7ab983/src/main/java/org/openlogisticsfoundation/neone/model/Subscription.java#L19

Example:

{
  "@context": {
    "cargo": "https://onerecord.iata.org/ns/cargo#",
    "api": "https://onerecord.iata.org/ns/api#"
  },
  "@type": "api:Subscription",
  "api:hasContentType": "application/ld+json",
  "api:hasDescription": "Need updates for shipment tracking",
  "api:hasSubscriber": {
    "@id": "http://localhost:8080/logistics-objects/_data-holder"
  },
  "api:hasTopicType": {
    "@id": "api:LOGISTICS_OBJECT_IDENTIFIER"
  },
  "api:includeSubscriptionEventType": [
    {
      "@id": "api:LOGISTICS_OBJECT_UPDATED"
    },
    {
      "@id": "api:LOGISTICS_OBJECT_CREATED"
    },
    {
      "@id": "api:LOGISTICS_EVENT_RECEIVED"
    }
  ],
  "api:hasTopic": {
    "@id": "https://1r.example.com/logistics-objects/1a8ded38-1804-467c-a369-81a411416b7c"
  }
}