NuGet discovers credentials providers installed using .NET tools

[Nigusu-Allehu]

Follow #13242 and make sure NuGet discovers credential providers installed using .NET tools.
dotnet tool install <provider package name> --global should install the tool and add its path to the PATH environmental varibale. Iterate through all the paths in PATH and all the files in the path to find the plugins. By design, we expect these plugins to be named nuget-plugin*.

[dotnet-policy-service]

@Nigusu-Allehu Issue is missing Type label, remember to add a Type label