Extension: Drag and drop ordering for lesson / chapter / parts

### Is your feature request related to a problem?

TutorialKit VSCode extension does not support ordering items with drag and drop.

### Describe the solution you'd like.

Add support for drag and drop re-ordering. 

### Describe alternatives you've considered.

-

### Additional context

Split from https://github.com/stackblitz/tutorialkit/issues/144