The optional default maximum time, specified when registering the activity type, before which a worker processing a task must report
            progress by calling RecordActivityTaskHeartbeat. You can override this default when scheduling a task through the
            ScheduleActivityTaskDecision. If the activity worker subsequently attempts to record a heartbeat or returns a result, the
            activity worker receives an UnknownResource fault. In this case, Amazon SWF no longer considers the activity task to be valid; the
            activity worker should clean up the activity task. The valid values are integers greater than or equal to 0. An integer value can be
            used to specify the duration in seconds while NONE can be used to specify unlimited duration.
             
            
Constraints:
 Declaration Syntax
 Declaration Syntax| C# | 
public string DefaultTaskHeartbeatTimeout { get; set; }