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

@@ -266,6 +266,10 @@ New APIs and options
 
   * :c:func:`sys_count_bits`
 
+* Video
+
+  * :c:member:`video_format.size` field
+
 * Task Watchdog
 
   * :kconfig:option:`CONFIG_TASK_WDT_DUMMY`