input: Write a python function to manage candies and perform operations like adding, removing, and listing candies.
  assert candies.get_list_candy() == ["sourpatchkids", "mars"]
  candies.add_candy("kitkat", 3)
  assert candies.get_list_candy() == ["sourpatchkids", "mars", "kitkat"]
  candies.remove_candy("mars")
  assert candies.get_list_candy() == ["sourpatchkids", "kitkat"]
output: class CandyManager:
      def __init__(self):
          self.candies = {"sourpatchkids": 5, "mars": 2}
  
      def add_candy(self, candy_name, quantity):
          if candy_name in self.candies:
              self.candies[candy_name] += quantity
          else:
              self.candies[candy_name] = quantity
  
      def remove_candy(self, candy_name):
          if candy_name in self.candies:
              del self.candies[candy_name]
  
      def get_list_candy(self):
          return list(self.candies.keys())
  
  candies = CandyManager()