Fix document number field duplication during verification

[tramuntanal]

🎩 What? Why?

The changes in last version made the document number field being duplicated in the user verification form. One field was rendered for the :id_document attribute and another was rendered for the :document_number attribute. The handler was still working whichever field was set.

To avoid the field duplication this PR removes the :document_number attribute and extracts that field in the constructor if present.

Binstubs for rspec and rubocop has also been added.

📌 Related Issues

• Fixes Adapt handler to initiatives #23

📋 Subtasks

• Add documentation regarding the feature
• Add tests

[laurajaime]

Good solution!