[1pt] Implement methods for Author and Game-Team member #3

[Kaghenimbale]

Implement methods:
add_item method in the Author class
should take an instance of the Item class as an input
should add the input item to the collection of items
should add self as a property of the item object (by using the correct setter from the item object)
can_be_archived?() in the Game class
should override the method from the parent class
should return true if parent's method returns true AND if last_played_at is older than 2 years
otherwise, it should return false