doc: releases: 4.3: Add CoAP client callback data migration and notes

Add a migration note entry for the CoAP client response callback signature
change and add an entry to the release notes for the new struct type.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

Author: pdgendt

doc/releases/migration-guide-4.3.rst

@@ -184,6 +184,9 @@ Power management
 Networking
 **********
 
+* The :c:type:`coap_client_response_cb_t` signature has changed. The list of arguments
+  is passed as a :c:struct:`coap_client_response_data` pointer instead.
+
 * The HTTP server now respects the configured ``_config`` value. Check that
   you provide applicable value to :c:macro:`HTTP_SERVICE_DEFINE_EMPTY`,
   :c:macro:`HTTPS_SERVICE_DEFINE_EMPTY`, :c:macro:`HTTP_SERVICE_DEFINE` and

doc/releases/release-notes-4.3.rst

@@ -209,6 +209,10 @@ New APIs and options
 
 * Networking
 
+  * CoAP
+
+    * :c:struct:`coap_client_response_data`
+
   * Sockets
 
     * :c:func:`zsock_listen` now implements the ``backlog`` parameter support. The TCP server