DOCS Add blurbs about several new features to 4.11 changelog

I figured I'd write this while these changes are fairly fresh in my mind, and save someone else the trouble.
Obviously if there's some procedure ormpolicy for writing release notes that I'm not following here feel please let me know and feel free to close this PR.

Refer to silverstripe/silverstripe-admin#1251 for preview PRs, #10204 for the `GridFieldComponent` stuff, and silverstripe/silverstripe-elemental#913 for changes to elemental search indexing.

There are some extra new lines in here that I can't remove from the GitHub editor - but I expect there will be other requested changes so I'll clean that up at the same time.

docs/en/04_Changelogs/4.11.0.md

@@ -5,6 +5,8 @@
 - [Regression test and Security audit](#audit)
 - [Dropping support for PHP 7.3](#phpeol)
 - [Features and enhancements](#features-and-enhancements)
+  - [Preview any DataObject in any admin section](#cms-preview)
+  - [Other features](#other-features)
 - [Bugfixes](#bugfixes)
 - [Internal API changes](#internal-api-changes)
 
@@ -21,6 +23,21 @@ In accordance with our [PHP support policy](/Getting_Started/Server_Requirements
 
 ## Features and enhancements {#features-and-enhancements}
 
+### Preview any DataObject in any admin section {#cms-preview}
+
+The CMS preview panel has historically on been available on `Versioned` `DataObjects` in the Pages admin section. This has now been expanded to allow any `DataObject`(regardless of whethwr they jse the`Versioned` extension) to be previewed in any section of the CMS.
+
+This can be used to allow content authors to see the content they are creating in the context it will be presented to users. Example use cases include previewing `DataObjects` which belong to a page (e.g. the [dnadesign/silverstripe-elemental module](https://github.com/silverstripe/silverstripe-elemental) allows previewing elemental blocks which are not inline-editable), and previewing `DataObjects` in a custom admin section, such as email or system-generated PDF templates.
+
+The [Preview Documentation](https://docs.silverstripe.org/en/4/developer_guides/customising_the_admin_interface/preview/) has been updated with code examples which show how to enable CMS preview on `DataObjects` in a couple of different scenarios.
+
+
+### Other new features {#other-features}
+
+- A new [AbstractGridFieldComponent](https://api.silverstripe.org/4/SilverStripe/Forms/GridField/AbstractGridFieldComponent.html) class has been added to make it easier to globally add fundamental functionality to `GridFieldComponent`s. All classes packed with the Silverstripe framework which implement the `GridFieldComponent` interface are subclasses of the new abstract class, making them all `Injectable`. Maintainers of third-party packages which include classes that implement `GridFieldComponent` are encouraged to subclass the `AbstractGridFieldComponent` abstract class.
+- New options have neen added to the [dnadesign/silverstripe-elemental module](https://github.com/silverstripe/silverstripe-elemental) to control what content is indexed for searching elemental blocks. see [the documentation](https://github.com/silverstripe/silverstripe-elemental/blob/4/docs/en/searching-blocks.md) for details.
+
+
 
 ## Bugfixes {#bugfixes}