input: Write a python function to insert an item into a list at a specified index using the list.insert() method.
  assert insert_item([1, 2, 3, 4, 5], 2, 10) == [1, 2, 10, 3, 4, 5]
  assert insert_item([10, 20, 30, 40, 50], 0, 5) == [5, 10, 20, 30, 40, 50]
  assert insert_item([5, 15, 25, 35, 45], 4, 100) == [5, 15, 25, 35, 100, 45]
output: def insert_item(lst, index, item):
      lst.insert(index, item)
      return lst