Add option to generate public/internal setters for generated models for Testing scenarios

Hi,

I would like to be able to stub a client generated by Kiota. But, currently, the models has private setters, like this:

I use OpenAPI spec: `kiota search microsoft.com:cognitiveservices-NewsSearch`

```csharp
namespace NewsSearch.Sdk.Models {
public class NewsTopic : Thing, IParsable {
/// A Boolean value that indicates whether the topic is considered breaking news. If the topic is considered breaking news, the value is true.
public bool? IsBreakingNews { get; private set; }
/// The URL to the Bing News search results for the search query term
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
public string? NewsSearchUrl { get; private set; }
#nullable restore
#else
public string NewsSearchUrl { get; private set; }
#endif
/// Defines a search query.
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
public NewsSearch.Sdk.Models.Query? Query { get; set; }
#nullable restore
#else
public NewsSearch.Sdk.Models.Query Query { get; set; }
#endif

// omitted
}
}

```

I would like to suggest adding a configuration that allows control aspects of model generation.

Thank you, I appreciate your work.

The issue shows generated C# model properties from the NewsSearch OpenAPI example, but names no generator files or tests. Start by locating Kiota's C# model-generation entry point and its existing configuration options; done means a documented option controls whether generated model setters are private, internal, or public, with coverage for the selected behavior.

Written by the indexing model from the issue text.