Prevent a generic resource to be created with a type from the Nexus vocabulary

[imsdu]

Motivation
The resource endpoint is very permissive as it can accept almost any valid json-ld payload to create a resource.
This can cause some problems as someone can create what should be a schema or a view with this endpoint: the resource then has the correct json-ld type but is still considered a generic resource and extra validation is not applied.

Ex:

• Import resolution for schemas
• Creation of the index and validation of the mapping/settings for Elasticsearch views

Acceptance criteria

1. When attempting to create a generic resource when one of the types belongs to the Nexus vocabulary (so a type starting with https://bluebrain.github.io/nexus/vocabulary/), an error is returned

Implementation notes
This error must be translated as an Akka rejection in ResourcesRoutes