Fix: allow CTkSwitch.configure() to accept 'onvalue' and 'offvalue'

[fredmain]

Description

This pull request fixes an issue in the CTkSwitch widget where the onvalue and offvalue parameters could only be set during initialization, but not via the configure() method.

Trying to use .configure(onvalue=..., offvalue=...) would raise a ValueError due to missing handling for those parameters in the method.

Reproduction

import customtkinter

root = customtkinter.CTk()
s = customtkinter.CTkSwitch(root)
s.configure(onvalue='manual', offvalue='automatic')  # 💥 ValueError before this fix
s.pack()
root.mainloop()

Fix

I added handling for onvalue and offvalue inside the configure() method of CTkSwitch, following the same pattern used for other supported keyword arguments like text, state, and variable.
Let me know if I should add test cases or adjust anything.