Add documentation examples for overridden-final-method checker

Author: mbyrnepr2

doc/data/messages/o/overridden-final-method/bad.py

@@ -0,0 +1,12 @@
+from typing import final
+
+
+class Base:
+    @final
+    def my_method(self):
+        pass
+
+
+class Subclass(Base):
+    def my_method(self):  # [overridden-final-method]
+        pass

doc/data/messages/o/overridden-final-method/good.py

@@ -0,0 +1,12 @@
+from typing import final
+
+
+class Base:
+    @final
+    def my_method(self):
+        pass
+
+
+class Subclass(Base):
+    def my_other_method(self):
+        pass