input: Write a python function to create a list of employees sorted by salary in descending order.
  assert [e.emp_id for e in sort_employees_by_salary([Employee(1, 'Alice', 'HR', 50000), Employee(2, 'Bob', 'IT', 60000), Employee(3, 'Charlie', 'Finance', 55000)])] == [2, 3, 1]
  assert [e.emp_id for e in sort_employees_by_salary([Employee(4, 'David', 'HR', 45000), Employee(5, 'Eve', 'IT', 70000), Employee(6, 'Frank', 'Finance', 65000)])] == [5, 6, 4]
output: def sort_employees_by_salary(employees):
      return sorted(employees, key=lambda e: e.salary, reverse=True)