[3.13] gh-126008: Improve docstrings for Tkinter cget and configure methods (GH-133303) (GH-137661)

* Explain the behavior of Widget.configure() depending on arguments.
* Unify descriptions.
* Replace "resource" with "option".
(cherry picked from commit 027cacb67ce1b16a96a6a2866299803eff16a4a6)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>