[FrameworkBundle] Update cache_dir config

Signed-off-by: Quentin Devos <4972091+Okhoshi@users.noreply.github.com>

reference/configuration/framework.rst

@@ -1511,6 +1511,19 @@ cache_dir
 The directory where routing information will be cached. Can be set to
 ``~`` (``null``) to disable route caching.
 
+.. deprecated:: 7.1
+
+    Setting the ``cache_dir`` option is deprecated since Symfony 7.1. The routes
+    are now always cached in the ``%kernel.build_dir%`` directory. If you want
+    to disable route caching, set the ``ignore_cache`` option to ``true``.
+
+ignore_cache
+............
+
+**type**: ``boolean`` **default**: ``false``
+
+When this option is set to ``true``, routing information will not be cached.
+
 secrets
 ~~~~~~~