Support optional parameters

[XDracam]

[Hub]
public interface IExampleHub {
    public Task DoSomething(int optional = 3);
    public Task DoSomething2(string? optional = null);
}

This hub currently generates:

export type IExampleHub = {
    doSomething(optional: number): Promise<void>;
    doSomething2(optional: string): Promise<void>;
}

Which is awkward, because now I have to provide parameters that are entirely unnecessary in the backend API.

Please add support for optional parameters in hub methods. Or, if you wish and can give me entry points, I can work on a PR as well.