Dialogs > The Next and Back buttons should be removed when there is no steps

When creating a document model, the modal have 3 buttons:

• cancel
• next, which brings you to the document config page but not in the modal (and so you may think that you've missed a step)
• back, which brings you in a root menu that doesn't make any sense as you can access these entries from the tree.

The next and back buttons are disturbing and make this simple first feature surprising.

The back button should be removed when there is no step before, and the next button should be replaced by a "Start configuring" or "Start customization" or a simple "ok".

NB: This behavior is not only in Document Creation modal but we should start by this screen, as it's one of the first things people do in Studio.