input: Write a python function to generate a sequence of numbers in a given range separated by commas.
  assert generate_sequence(10, 20) == '10, 11, 12, 13, 14, 15, 16, 17, 18, 19'
  assert generate_sequence(5, 8) == '5, 6, 7, 8'
  assert generate_sequence(1, 3) == '1, 2, 3'
output: def generate_sequence(start, end):
      return ', '.join(str(i) for i in range(start, end))