add more exception type (#2357)

Author: KayMKM

sdk/csharp/libraries/microsoft.bot.builder.solutions.skills/SkillException.cs

@@ -14,6 +14,21 @@ public enum SkillExceptionType
         /// </summary>
         AccountNotActivated,
 
+        /// <summary>
+        ///  Bad Request returned when calling external APIs
+        /// </summary>
+        APIBadRequest,
+
+        /// <summary>
+        ///  Unauthorized returned when calling external APIs
+        /// </summary>
+        APIUnauthorized,
+
+        /// <summary>
+        ///  Forbidden returned when calling external APIs
+        /// </summary>
+        APIForbidden,
+
         /// <summary>
         /// Other types of exceptions
         /// </summary>