NuGet.CommandLineXPlat should assert absolute path for dotnet list package

[Nigusu-Allehu]

We currently have dotnet list package implemented so that the NuGet side always expects an absolute path. However, we do not assert this. We should assert it and print out a clear error message if an absolute path is not provided. In addition, we should also add an integration test for this command: https://github.com/NuGet/NuGet.Client/tree/dev/test/NuGet.Core.FuncTests/Dotnet.Integration.Test.