Add a dotnet nuget config command

[heng-liu]

NuGet Product(s) Involved

dotnet.exe

The Elevator Pitch

Add a dotnet nuget config command to manage NuGet configuration settings.

Tracking issues:

• Spec: Write a spec for dotnet nuget config command #12297
• Implement dotnet nuget config path(seasons of giving): Suggestion: NuGet config -list command to list configuration file locations #8420
• NuGet config command doesn't check if the key is valid: NuGet config command doesn't check if the key is valid #12345
• Implement dotnet nuget config get
• Implement dotnet nuget config set/unset

[heng-liu]

Close this as a duplicate of #12469