Show subcommand help instead of main dotnet nuget trust command help for all cases

[erdembayar]

Details about Problem

NuGet product used (dotnet.exe):

Product version:

Worked before? If so, with which NuGet version: N/A

Repro steps and/or sample project

Printing out help doesn't help at all unless the error itself has to do with a command, argument, or option being invalid.
Current experience show help for dotnet nuget is different from nuget.exe. It show help when there is a exception like InvalidOperationException even though it's nothing to do with a command, argument, or option being invalid

For example:

It adds red marked help even though it's not really needed.

Verbose Logs

[aortiz-msft]

Not a blocking issue for the new command, but something we'd like to improve shortly afterwards.

[erdembayar]

NuGet/NuGet.Client#3989 (comment)
NuGet/NuGet.Client#3989 (comment)
Registering sub-commands improves error handling, reading values for options/arguments instead of searching strings which can be error prone if not done right, help messages

[erdembayar]

nuget59 trusted-signers add .\newtonsoft.json.13.0.1-beta1.nupkg -Name NewtonAuthor333 -Author -config ..\nuget.config -AllowUntrustedRoot
dotnet nuget trust author NewtonAuthor333 .\newtonsoft.json.13.0.1-beta1.nupkg --configfile ..\nuget.config --allow-untrusted-root