Add test command to ensure the notebook runs

[94rain]

Describe your changes

Add test command to ensure the notebook runs:

• Convert ipynb files to py in the current folder with tempfile (which is more straightforward than converting py to ipynb and I can catch exceptions with exec(), like what I did for the clean command).
• Use exec(open(filename).read()) execute py files
• Use try-except block to catch exceptions
• Create a dict error_suggestion_dict to store exception handling suggestions.

Cases:

• Notebooks that can run: Finished executing {filename}, no error encountered
• Notebooks with ModuleNotFoundError, AttributeError, SyntaxError: provide suggestions: {error_type} encountered while executing the notebook: {err}. It is recommended to + [suggestion]
  • "ModuleNotFoundError": "create a virtualenv, and adding a requirements.txt with the package",
  • "AttributeError": "downgrade some libraries",
  • "SyntaxError": "check syntax",
• Notebooks with other errors: provide a link to the guide of debugging notebooks:

  {error_type} encountered while executing the notebook:  {err}
  Checkout how to debug notebooks: 
  https://docs.ploomber.io/en/latest/user-guide/debugging.html

  Issue ticket number and link

  Closes #6

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] I have added thorough tests (when necessary).
• [x] I have added the right documentation (when needed). Product update? If yes, write one line about this update.