input: Write a python function to add a student to a school.
  assert add_student_to_school(school, 'Alice', 90) == ['Alice']
  assert add_student_to_school(school, 'Bob', 85) == ['Alice', 'Bob']
  assert add_student_to_school(school, 'Charlie', 92) == ['Alice', 'Bob', 'Charlie']
output: def add_student_to_school(school, name, grade):
      if 'students' not in school:
          school['students'] = []
      school['students'].append({'name': name, 'grade': grade})
      return [student['name'] for student in school['students']]