added CTkConfirmationDialog

[ageorge95]

Hello, I have created a very simple ConfirmationDialog within the CustomTkinter framework.

If you think it is helpful you can merge it so that it is accessible to everyone 😊

Below is a usage example:

dialog = CTkConfirmationDialog(title="Quit", message="Do you really want to quit?").get_selection()
if dialog:
  pass # do stuff if the answer is OK (True)
else:
  pass # do other stuff if the answer is CANCEL (False)

(If I need to adapt it/ change it/ beautify it in order to merge it on the master branch let me know, I can dedicate some time to help with the merge)

[ageorge95]

Added a screenshot of the dialog window produced by the example code from the PR's description: