News dashboard: API and rendering of news stories on dashboard (#20416)

* Adding controller

* Lower case route to match other endpoints

* Adding service and typed output

* Renaming to NewsDashboard

* Moving more stuff to service

* Removing unused code

* Some refactoring in accordance with better architecture

* Created repository and mock data source for the news dashboard also display some data in the UI.

* Minor refactoring: naming, aligning with existing controller patterns.

* Update OpenApi.json.

* Update typed client sdk and types.

* Provide language to API endpoint, just in case we want to localize news in the future.

* Obsoleted configuration

* Moved mock data to mocks folder and updated repository to use the actual response model and service from the Api

* Prepared news repository with server data source.

* Rendered news items according to required group structure.
Added TODOs for remaining tasks.

* Fixed FE build issues.

* Update src/Umbraco.Core/Constants-Configuration.cs

* Fixed grid spacing, sanitize code and make the styles closer to the v13.

* Added container query and padding to the card body.

* Fix padding

* Fixed title according to priority.

* Relocated/renamed the news server data-source file

* Simplified the news repo/data-source classes

by extending `UmbControllerBase`, the host constructor is handled for us.

* Added `types.ts` export type files

* Refactored interface name + typing

* Added `uui-loader` component

* Tweaked styles, added box-shadow to cards

Added flexbox gap to the card body.

* Sorted import order

---------

Co-authored-by: Andy Butland <abutland73@gmail.com>
Co-authored-by: engjlr <enl@umbraco.dk>
Co-authored-by: leekelleher <leekelleher@gmail.com>

src/Umbraco.Core/Constants-Configuration.cs

@@ -57,6 +57,7 @@ public static partial class Constants
         public const string ConfigUserPassword = ConfigPrefix + "Security:UserPassword";
         public const string ConfigRichTextEditor = ConfigPrefix + "RichTextEditor";
         public const string ConfigPackageMigration = ConfigPrefix + "PackageMigration";
+        [Obsolete("No longer used in Umbraco. Scheduled to be removed in Umbraco 19.")]
         public const string ConfigContentDashboard = ConfigPrefix + "ContentDashboard";
         public const string ConfigHelpPage = ConfigPrefix + "HelpPage";
         public const string ConfigInstallDefaultData = ConfigPrefix + "InstallDefaultData";