Add entry to change log about CMSPageHistoryController deprecation. (#8508)

* Add entry to change log about CMSPageHistoryController deprecation.

* Correct typo #8508

* Tweaking CMS History controller changelog entry #8508

docs/en/04_Changelogs/4.3.0.md

@@ -7,6 +7,7 @@
  - Take care with `stageChildren()` overrides. `Hierarchy::numChildren() ` results will only make use of `stageChildren()` customisations that are applied to the base class and don't include record-specific behaviour.
  - New React-based search UI for the CMS, Asset-Admin, GridFields and ModelAdmins.
  - A new `GridFieldLazyLoader` component can be added to `GridField`. This will delay the fetching of data until the user access the container Tab of the GridField.
+ - `SilverStripe\VersionedAdmin\Controllers\CMSPageHistoryViewerController` is now the default CMS history controller and `SilverStripe\CMS\Controllers\CMSPageHistoryController` has been deprecated.
 
 ## Upgrading {#upgrading}
 
@@ -41,3 +42,23 @@ public function getCMSFields()
 }
 
 ```
+
+### Keep using the legacy `CMSPageHistoryController`
+
+To keep using the old CMS history controller for every page type, add the following entry to your YML config.
+
+```yml
+SilverStripe\Core\Injector\Injector:
+  SilverStripe\CMS\Controllers\CMSPageHistoryController:
+    class: SilverStripe\CMS\Controllers\CMSPageHistoryController
+```
+
+If you want to use both CMS history controllers in different contexts, you can implement your own _Factory_ class.
+```yml
+SilverStripe\Core\Injector\Injector:
+  SilverStripe\CMS\Controllers\CMSPageHistoryController:
+    factory:
+      App\MySite\MyCustomControllerFactory
+```
+
+[Implementing a _Factory_ with the Injector](/developer_guides/extending/injector/#factories)