``nuget.exe push *.nupkg`` doesn't push more than one file

The nuget.exe counterpart to https://github.com/NuGet/Home/issues/4393 where the dotnet.exe experience was fixed, but we didn't want to break nuget.exe outside of a major release.

https://github.com/NuGet/NuGet.Client/pull/3739#issuecomment-720481177

It turns out though, that extending push command for nuget.exe is rather not possible due to problems with backwards compatibility. There is some special ApiKey logic, which for cases where ApiKey is not specified, it assumes that second parameter is an ApiKey (https://github.com/NuGet/NuGet.Client/blob/dev/src/NuGet.Clients/NuGet.CommandLine/Commands/PushCommand.cs#L51-L58) This behaviour is also documented here https://docs.microsoft.com/en-gb/nuget/reference/cli-reference/cli-ref-push#examples.