doc: release-note-4.3: document size field added to video_format struct

Document introduction of the new size field inside video_format struct
as visible on the <zephyr/drivers/video.h> header.

Signed-off-by: Hugues Fruchet <[email protected]>

Author: hfruchet-st

doc/releases/release-notes-4.3.rst

@@ -276,6 +276,10 @@ New APIs and options
 
   * :c:macro:`__deprecated_version`
 
+* Video
+
+  * :c:member:`video_format.size` field
+
 .. zephyr-keep-sorted-stop
 
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