[Feature]: add dotnet nuget why to dotnet CLI

[kartheekp-ms]

NuGet Product(s) Involved

dotnet.exe

The Elevator Pitch

This is a tracking issue for feature request #11782

Design spec - dotnet nuget why command (Spec PR)

Proof of concept: https://github.com/NuGet/NuGet.Client/tree/pragnya17-dotnet-nuget-why (compare)

Additional Context and Details

• Add dotnet nuget why command - https://github.com/NuGet/Client.Engineering/issues/2862
• Add docs to dotnet/docs - Add docs for dotnet nuget why #13499
• Add integration to dotnet/sdk - https://github.com/NuGet/Client.Engineering/issues/2861

[kartheekp-ms]

proof of concept at: https://github.com/NuGet/NuGet.Client/tree/pragnya17-dotnet-nuget-why