Make catalog information DCAT-AP/VL compliant

[rorlic]

Is your feature request related to a problem? Please describe.
Currently, when adding a new catalog using /admin/api/v1/dcat the catalog is identified using a newly created GUID.
This GUID is currently not used except for as a way to delete the catalog information.
The DCAT-AP/VL requires a dc:identifier for a catalog and currently we do not add one.

Describe the solution you'd like
we can reuse the generated GUID as the catalog identifier.
Please add a statement to the catalog for the generated identifier. E.g.

@prefix dcat:     <http://www.w3.org/ns/dcat#> .
@prefix dc:       <http://purl.org/dc/terms/> .
@prefix rdfs:     <http://www.w3.org/2000/01/rdf-schema#> .

[] a dcat:Catalog ;
  ...
  dc:identifier "2a896d35-8c72-4723-83b3-add9b1be96aa"^^rdfs:Literal .

[rorlic]

In addition, please also add the following for each dataset (= LDES):

[] a dcat:Dataset
  ...
  dc:conformsTo <https://w3id.org/tree/specification>, <https://w3id.org/ldes/specification> .

<https://w3id.org/tree/specification> a dc:Standard .
<https://w3id.org/ldes/specification> a dc:Standard .

i.e. add 2 dc:conformsTo statements to each Dataset.

[rorlic]

In addition, add an identifier to each Dataset and each DataService:

[] a dcat:Dataset
  ...
  dc:identifier "https://example.org/observations"^^rdfs:Literal .

[] a dcat:DataService
  ...
  dc:identifier "https://example.org/observations/by-location"^^rdfs:Literal .

You can use the full URL of the LDES and view as a string (not an URI).

[rorlic]

Finally, add an endpoint description to each DataService (view) and mark it as a rdfs:Resource:

[] a dcat:DataService
  ...
  dcat:endpointDescription <http://localhost:8080/v1/swagger?urls.primaryName=base> .

<http://localhost:8080/v1/swagger?urls.primaryName=base> a rdfs:Resource .

The URI of the dcat:endpointDescription can be constructed by taking the server settings:
{ldes-server.host-name}{springdoc.swagger-ui.path}?urls.primaryName=base

[rorlic]

for now use a fixed value for all dcat:endpointDescription, i.e.

...
dcat:endpointDescription <https://semiceu.github.io/LinkedDataEventStreams/> .