text: Title: Specify template location for ploomber scaffold
  Body: It would be nice to specify the template location, whether a url or local directory, when calling ploomber scaffold. 
  
  ploomber scaffold --from-template https://github.com/user/my-template
  ploomber scaffold --from-template ~/custom_template
  
  It'd also be nice to be able to set the default template from a user / all users (when using a system install of python) like:
  
  ploomber scaffold --set-template https://github.com/user/my-template
  