[React] 다른 board끼리의 움직임

1. 먼저 sourceboard의 복사본을 만들어줘야한다.

const sourceBoard = [...allBoards[source.droppableId]]

2. target도 만들자

const destinationBoard = [...allBoards[destination.droppableId]]

3. 지우고 추가하고 하자

sourceBoard.splice(source.index, 1);
destinationBoard.splice(destination?.index, 0, draggableId)

4. 모두 출력하자

return {
  ...allBoards,
  [source.droppableId]: sourceBoard,
  [destination.droppableId]: destinationBoard,
}