chore(changelog): list radio validation feature (#12659)

Co-authored-by: Simeon Simeonoff <[email protected]>

Author: SisIvanova

CHANGELOG.md

@@ -13,6 +13,8 @@ All notable changes for each version of this project will be documented in this
     - **Breaking Change** The `onDensityChanged` output has been renamed to `densityChanged` to not violate the no on-prefixed outputs convention. All components expolsing this event are affected. Automatic migrations are available and will be applied on `ng update`.
  - `IgxCarousel`
     - **Breaking Change** The `onSlideChanged`, `onSlideAdded`, `onSlideRemoved`, `onCarouselPaused` and `onCarouselPlaying` outputs have been renamed to `slideChanged`, `slideAdded`, `slideRemoved`, `carouselPaused` and `carouselPlaying` to not violate the no on-prefixed outputs convention. Automatic migrations are available and will be applied on `ng update`.
+- `IgxRadio`, `IgxRadioGroup`
+    - Added component validation along with styles for invalid state
 
 
 ## 15.0.1