Added UI Toolkit Progress

Src/Core/Extensions/HttpClient.cs

@@ -11,6 +11,10 @@ namespace BITKit
 		public static async UniTask<string> PostJsonAsync(this HttpClient self, string requestUrl, object value , CancellationToken cancellationToken=default)
 		{
 			var json = JsonConvert.SerializeObject(value);
+			if (value is string j)
+			{
+				json = j;
+			}
 			var content = new StringContent(json, Encoding.UTF8, "application/json");
 			var response =await self.PostAsync(requestUrl, content, cancellationToken);
 			return await response.Content.ReadAsStringAsync();