Allow to modify the JsonSerializerOptions

Could we provide a way to change the default json options of JsonSerializer?
```
public static async Task GetAndDeserializeAsync(this HttpClient client, string requestUri, ITestOutputHelper output = null)
{
HttpResponseMessage obj = await client.GetAsync(requestUri, output);
obj.EnsureSuccessStatusCode();
string text = await obj.Content.ReadAsStringAsync();
output?.WriteLine("Response: " + text);
return JsonSerializer.Deserialize(text, Constants.DefaultJsonOptions);
}
```

Start at GetAndDeserializeAsync and trace Constants.DefaultJsonOptions to understand where the default settings are applied. Determine how callers should provide or change JsonSerializerOptions, then verify that deserialization uses those options without breaking the existing default behavior.

Written by the indexing model from the issue text.