added to Migration guide

Signed-off-by: alexander <[email protected]>

migration/Jazzy.rst

@@ -189,3 +189,9 @@ They have been consolidated into a single one:
 
 The ``local_namespace`` parameter has been removed and is now automatically set to the node's name (which is what the second removed constructor did).
 Parameters ``parent_namespace`` / ``use_sim_time`` both provide default values to maintain the ability of creating a ``Costmap2DROS`` object by just specifying a name.
+
+New Plugin Container Layer
+**************************
+
+In `PR #4781 <https://github.com/ros-navigation/navigation2/pull/4781>`_ a costmap layer plugin type was added to support the grouping of different costmap layers under a single costmap layer. This would allow for different isolated combinations of costmap layers to be combined under one parent costmap instead of the current implementation which would indiscriminately combine all costmap layers together. 
+