message: Add leetcode monotonic array code
diff: class Solution:
  def isMonotonic(self, A: List[int]) -> bool:
  + #an array is monotonic if it is either increasing or decreasing, so we check if the array is equal to
  + #its sorted version in either descending order or ascending order. If yes return True
  + #else return False.
  if A==sorted(A):
  return True
  if A==sorted(A,reverse=True):
  