minor #15353 [Security] Document logout.target (MatTheCat)

This PR was submitted for the 5.x branch but it was merged into the 4.4 branch instead.

Discussion
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[Security] Document logout.target

Fixes #15352 and #5751

Commits
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3826ca9 Document logout.target

Author: javiereguiluz

reference/configuration/security.rst

@@ -593,6 +593,13 @@ required by the :class:`Symfony\\Component\\Security\\Core\\User\\UserInterface`
 The path which triggers logout. If you change it from the default value ``/logout``,
 you need to set up a route with a matching path.
 
+target
+~~~~~~
+
+**type**: ``string`` **default**: ``/``
+
+The route, path or URL to redirect to after logout.
+
 success_handler
 ~~~~~~~~~~~~~~~
 
@@ -601,6 +608,8 @@ success_handler
 The service ID used for handling a successful logout. The service must implement
 :class:`Symfony\\Component\\Security\\Http\\Logout\\LogoutSuccessHandlerInterface`.
 
+If it is set, ``target`` will be ignored.
+
 .. _reference-security-logout-csrf:
 
 csrf_parameter