Propose @ORD vocabulary for backlinks to ORD metadata

[Fannon]

Proposal is to be able to create a connection (potentially back) to the ORD layer, where the API, Event Resources and Entitles are also described, with shared high-level properties (like lifecycle, taxonomy) and relationships across concepts.

If we want to import a CSN Interop document to add it as an "Integration Dependency", we also need to know its ORD ID. If the document already contains it, that makes the import of CSN much easier.

Open Questions

• Should we allow for meta.document annotations to ORD IDs? Depending on the granularity of the content in the CSN Document, it could be possible to link the entire document to ORD API Resources (if only one service is described) or ORD Data Product (if the scope of the document is to describe the Data Product data model).

Example

{ // ..
  "definitions": {
    "AirlineService": {
      "kind": "service",
      "doc": "This is describing the service that exposes the CDS entities through an API. Which protocol is used could be provided through `@protocol` today. For CSN Interop, we consider introducing an aligned, more flexible `@Service.api` annotation",
      "@ORD.ordIds": ["sap.foo:apiResource:AirlineDeltaShare:v1"],
      ]
    },
    "AirlineService.Airline": {
      "kind": "entity",
      "doc": "Human readable description of the entity, in **markdown**.",
      "@ORD.ordIds": ["sap.foo:entityType:Airline:v1"],