Create a dictionary named grades where the keys are student names $($strings$)$ and the values are lists of grades $($integers$).$

Add a new student to the dictionary with a list of grades.

Update the grades for an existing student.

Calculate and print the average grade for each student.

Identify and print the student with the highest average grade.

Requirements:

Your program should define the dictionary and include functions to add, update, and calculate averages.

Ensure your program handles cases where a student does not exist when updating grades.