doc: release-note-4.3: Add video format estimation helper

Mention a new video_estimate_fmt_size helper.

Signed-off-by: Phi Bang Nguyen <[email protected]>

Author: ngphibang

doc/releases/release-notes-4.3.rst

@@ -279,6 +279,7 @@ New APIs and options
 * Video
 
   * :c:member:`video_format.size` field
+  * :c:func:`video_estimate_fmt_size`
 
 .. zephyr-keep-sorted-stop