Add a new step to the Enterprise Beginner tutorial about using Form Builder.

Tentative extent:

• Create a Form and then embed it in a Form block in the right column of front page, OR create it on the fly
• The form is a newsletter signup, containing:
  • name
  • email
  • captcha (maybe also configure it according to https://doc.ezplatform.com/en/latest/guide/extending_form_builder/#captcha-field)
  • dropdown/select with interest
• Configure form submissions (email notification if not too complicated for beginner)
• Add design for the block/configuration page