Fluent interface for System.CommandLine

Hello everybody,

I have written a fluent interface for the System.CommandLine

Below is the sample from your wiki in fluent form.

```csharp
static Task Main(string[] args)
=> args.ArgsCommandBuilder("My sample app")
.Option("--int-option", 42, "An option whose argument is parsed as an int")
.Option("--bool-option", default, "An option whose argument is parsed as a bool")
.Option("--file-option", default, "An option whose argument is parsed as a FileInfo")
.OnRootCommand((intOption, boolOption, fileOption) =>
{
Console.WriteLine($"The value for --int-option is: {intOption}");
Console.WriteLine($"The value for --bool-option is: {boolOption}");
Console.WriteLine($"The value for --file-option is: {fileOption?.FullName ?? "null"}");
})
.RunAsync();
```
More doc, code, tests and samples can be found on [my github side](https://github.com/EifelMono/EifelMono.ConsoleApp)

I would like to bring this in these project if you think it is useful for others and fits in this project