Create different API sections in DocFX based documentations

[pepinho24]

Is your feature request related to a problem? Please describe.
The DocumentProcessing team distributes two types of assemblies - targeting .NET Framework and targeting .NET Standard.

This leads to the necessity of a feature that would allow clients to review the API documentation for one or the other distribution.

Such a feature may benefit some desktop teams that have similar dual-distributions and have a DocFX-based API generation.

Describe alternatives you've considered

1. The existing /API to be split into API/net-standard and API/net-framework, similar to the api/server and api/client.