support cascade NuGet.Config

[vpenades]

Right now, gpr uses the current user NuGet.Config by default and nothing else.

But this is not the expected behavior, as explained here.

Ideally, all tools using NuGet.Config files should behave in the same way, so developers can use any tool, irrespective of the developer strategy to define the NuGet.Config files.

Having specific behaviours for a given tool would mean that in order to use a given tool, you need to rearchitect the config files specifically for that tool, preventing the usage of other tools.

Now, given that all the ecosystem is open source, I am sure that somewhere, there's some code to evaluate the final state of multiple nuget.config files, based on the aforementioned link.

I think this package is the one that does the magic.

NuGet.Configuration.Settings.LoadDefaultSettings(...) seems to be the method to load and resolve Nuget.Config files in the same way nuget.exe does.

[brgrz]

Adding this would also support single nuget.config at the top of the solution tree (solution with many projects) which currently does not work.