chore(changelog): add newly exposed output of the slider

Closes #6401

Author: Aleksandyr

CHANGELOG.md

@@ -68,6 +68,7 @@ All notable changes for each version of this project will be documented in this
     - `tickLabelsOrientation` input was added. Allows you to change the rotation of all tick labels from horizontal to vertical(toptobottom, bottomtotop).
     - `igxSliderTickLabel` directive has been introduced. Allows you to set a custom template for all tick labels.
     - `isContinuous` - input has been deleted. The option is not supported anymore.
+    - `onValueChanged` - new output has been exposed. This event is emitted at the end of every slide interaction. 
 
 - `IgxCarousel`:
     - `keyboardSupport` input is added, which can be used to enable and disable keyboard navigation