input: Write a python function to generate the first n numbers using a generator function.
  assert list(generate_numbers_n(5)) == [0, 1, 2, 3, 4]
  assert list(generate_numbers_n(3)) == [0, 1, 2]
  assert list(generate_numbers_n(0)) == []
output: def generate_numbers_n(n):
      for i in range(n):
          yield i