API for access grant information

### Description

As a service owner I would like to know what roles a logged inn user has that gave access to a given service in order to be able to write this to the data model and later use this as a audit log when receving the data in our end.

The solution should be provided as a .Net API in Altinn.App.Core Nuget package and be accessible as a injectable service to be used in custom code. Potentially later be extended as a configurable prefil source to be configured in Studio.

The implementation depends on this information being provided as a API by Autorization. This API does not currently exists today on Altinn 3. This was however a feature on Altinn 2 when requesting access to a link service (lenketjeneste).

### Additional Information

Request written on behalf of Skatt/Ruben Torp Kvasjord and their MVA service if further details are needed.

Begin by verifying whether the Autorization API now exposes the access-grant roles described in the issue; the issue says this dependency did not exist in Altinn 3. Then inspect the Altinn.App.Core Nuget package and its injectable-service entry points. Done means a usable .NET API for custom code that returns the logged-in user's roles for a given service.

Written by the indexing model from the issue text.