input: Write a python function to generate a string representation of the sum of a list of numbers.
  assert generate_sum_string([5, 3, 2, 6, 8]) == "5 + 3 + 2 + 6 + 8 = 24"
  assert generate_sum_string([1, 2, 3]) == "1 + 2 + 3 = 6"
  assert generate_sum_string([10, 20, 30]) == "10 + 20 + 30 = 60"
output: def generate_sum_string(numbers):
      total_sum = sum(numbers)
      num_str = " + ".join(map(str, numbers))
      return f"{num_str} = {total_sum}"