[0.5pt] Implement methods

[YKerroum]

• can_be_archived?() in the Item class
  • should return true if published_date is older than 10 years
  • otherwise, it should return false
• move_to_archive() in the Item class
  • should reuse can_be_archived?() method
  • should change the archived property to true if the result of the can_be_archived?() method is true
  • should do nothing if the result of the can_be_archived?() method is false