doc: migration-guide-4.1: Information about stack canaries

Add information about the changing in the stack canaries symbol behavior.

Signed-off-by: Flavio Ceolin <flavio.ceolin@gmail.com>

doc/releases/migration-guide-4.1.rst

@@ -21,6 +21,14 @@ Build System
 Kernel
 ******
 
+Security
+********
+
+* New options for stack canaries have been added, providing users with finer control over stack
+  protection. With this change, :kconfig:option:`CONFIG_STACK_CANARIES` no longer enables the
+  compiler option ``-fstack-protector-all``. Users who wish to use this option must now enable
+  :kconfig:option:`CONFIG_STACK_CANARIES_ALL`.
+
 Boards
 ******