docs: add link to config file changes

Author: kenjis

user_guide_src/source/changelogs/v4.3.0.rst

@@ -323,6 +323,7 @@ Changes
 
 - Config
     - All atomic type properties in ``Config`` classes have been typed.
+    - See :ref:`Upgrading <upgrade_430_config>` for information on changing the default values.
 - Changed the processing of Spark commands:
     - The ``CodeIgniter\CodeIgniter`` no longer handles Spark commands.
     - The ``CodeIgniter::isSparked()`` method has been removed.

user_guide_src/source/installation/upgrade_430.rst

@@ -236,6 +236,8 @@ Content Changes
 The following files received significant changes (including deprecations or visual adjustments)
 and it is recommended that you merge the updated versions with your application:
 
+.. _upgrade_430_config:
+
 Config
 ------