Add support for `initial` keyword

[WizzardMaker]

I'm using the initial keyword in some of my properties to limit the setting of them. This generator replaces initial with set, which is not the desired behaviour

Code:

public class X {
    public uint Id { get; init; }
}

Generated interface:

[GeneratedCode("AutomaticInterface", "")]
public partial interface IPlayer
{
    /// <inheritdoc />
    uint Id { get; set; }
}