[FR] Add whiteboard like in ClickUp

[JJger148]

1~3 main use cases of the proposed feature
I want to see appflowy with a whiteboard, like in Clickup (or Miro, or Excalidraw)

what types of users can benefit from using your proposed feature
Everyone who wants to think things through.
You wouldn't have to change your app to for a task

Additional context
https://clickup.com/

[savuori]

I'd like to add my reasons why I think this is an important feature. When developing something new you may come up with many ideas that are connected but do not belong to the note/page you're currently on. Switching between pages is cumbersome and seeing multiple notes at the same time is good when trying to see the bigger picture and trying to keep it coherent.