[Swagger Files] Endpoint-Object string instead of enum

[arnoweiss]

The Endpoint-object (as used by the AssetAdministrationShellDescriptor and SubmodelDescriptor) is denoted as a 128-char string in the json-schemas on swagger-hub. However, p. 82 of DotAAS-2 (IDTA 01002-3-0) restricts it to an enum.

There should be a concious decision which is intended.