moves a task to a new position
| sid | string | number | the id of the task to move | 
| tindex | number | the index of the position that the task will be moved to  (the index within a branch)  | 
| parent | string | number | the parent id. If specified, the tindex will  refer to the  index in the  'parent' branch  | 
| boolean | void | returns `false` if the action has been canceled using onBeforeTaskMove, returns `undefined` otherwise | 
const tasks = {
  data:[
     {id:"p_1", text:"Project #1", start_date:"01-04-2023", duration:18, 
     open:true},
     {id:"t_1", text:"Task #1", start_date:"02-04-2023", duration:8,
     parent:"p_1"},
     {id:"t_2", text:"Task #2", start_date:"11-04-2023", duration:8,
     parent:"p_1"}
   ]
};
gantt.init("gantt_here");
gantt.parse(tasks);
 
gantt.moveTask("t_1", 1); //-> after such a move, the task "t_1" will have the root level