Add support for wildcards when pushing

[jcansdale]

As suggested by @SDLionas

I would imagine the wildcard **/*.nupkg would work the same way as nuget push **/*.nupkg (https://docs.microsoft.com/en-us/nuget/reference/cli-reference/cli-ref-push). It should push all NuGet packages in all subdirectories. You don't need to hardcode names (for example, {ProjectName}/bin/Release/{PackageName}.{Version}.nupkg) or version number (which you need to remember to increment with each build).