Suggestion: Add corner_radius to button(s)

[rebeccaMozand]

I noticed that the corner_radius argument is available in the class (ctkmessagebox.py, line 48), but it is only applied to the frame (as self.round_corners), but not to the buttons. I would like my buttons to have the same corner_radius.
I think you could maybe add that in line 251-270 where you define the buttons? Or is there a specific reason that you chose not to?

I already made a workaround for myself where I redefine the buttons in a child class with self.button1.configure(corner_radius=x) etc, but I thought it would be neat to have in the library itself.