input: Write a python function to generate random numbers within a given range using randint.
  assert isinstance(random_number_generator(5, 15), int)
  assert 5 <= random_number_generator(5, 15) <= 15
  assert random_number_generator(1, 10) != random_number_generator(1, 10)
output: import random
  
  def random_number_generator(start, end):
      return random.randint(start, end)