If set, specifies the default maximum time before which a worker processing a task of this type must report progress by calling
            RecordActivityTaskHeartbeat. If the timeout is exceeded, the activity task is automatically timed out. This default can be overridden
            when scheduling an activity task using 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; }