doc: releases: Add runtime changes to release notes

Add runtime observers static allocation feature to release notes.

Signed-off-by: Rodrigo Peixoto <rodrigopex@gmail.com>

Author: rodrigopex

doc/releases/migration-guide-4.2.rst

@@ -514,13 +514,6 @@ Video
 Other subsystems
 ****************
 
-ZBus
-====
-
-* The function :c:func:`zbus_chan_add_obs` now requires a :c:struct:`zbus_observer_node` as an argument,
-  which was previously allocated through :c:func:`k_malloc` internally. The structure must remain valid
-  in memory until :c:func:`zbus_chan_rem_obs` is called.
-
 Modules
 *******
 

doc/releases/release-notes-4.2.rst

@@ -237,6 +237,19 @@ New APIs and options
 
   * :kconfig:option:`CONFIG_LV_Z_COLOR_MONO_HW_INVERSION`
 
+* ZBus
+
+  * Runtime observers can work without heap. Now it is possible to choose between static, dynamic,
+    and none allocation for the runtime observers nodes.
+  * Runtime observers using :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_NONE` must use
+    the new function :c:func:`zbus_chan_add_obs_with_node`.
+
+  * :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_DYNAMIC`
+  * :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_STATIC`
+  * :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_ALLOC_NONE`
+  * :kconfig:option:`CONFIG_ZBUS_RUNTIME_OBSERVERS_NODE_POOL_SIZE`
+
+
 New Boards
 **********