Notify API breaks (#2086) (#2151)

* Notify API breaks

API breaks introduced in ros2/rclcpp#1612

Signed-off-by: Mauro Passerino <mpasserino@irobot.com>

* Address PR suggestions

Signed-off-by: Mauro Passerino <mpasserino@irobot.com>

Co-authored-by: Mauro Passerino <mpasserino@irobot.com>
(cherry picked from commit 9b74059)

Co-authored-by: mauropasse <mauropasse@hotmail.com>

source/Releases/Release-Humble-Hawksbill.rst

@@ -226,6 +226,22 @@ For more details, see `REP 2007 <https://ros.org/reps/rep-2007.html>`_.
 
 For more details, please refer to this `pull request <https://github.com/ros2/rclcpp/pull/1723>`_.
 
+``add_to_wait_set`` method from ``Waitable`` class changes its return type from ``bool`` to ``void``
+""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+Before, classes derived from ``Waitable`` overriding ``add_to_wait_set`` were returning false when failing to add elements to the wait set, so the caller had to check this return value and throw or handle the error.
+This error handling should now be done directly on ``add_to_wait_set`` method, throwing if necessary.
+It is not required to return anything if no errors happened.
+Thus, this is a breaking change for downstream uses of ``Waitable``.
+
+See `ros2/rclcpp#1612 <https://github.com/ros2/rclcpp/pull/1612>`__ for more details.
+
+``get_notify_guard_condition`` method return type from ``NodeBaseInterface`` class changed
+""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
+Now ``rclcpp`` uses the ``GuardCondition`` class wrapper around ``rcl_guard_condition_t``, so ``get_notify_guard_condition`` returns a reference to the node's ``rclcpp::GuardCondition``.
+Thus, this is a breaking change for downstream uses of ``NodeBaseInterface`` and ``NodeBase``.
+
+See `ros2/rclcpp#1612 <https://github.com/ros2/rclcpp/pull/1612>`__ for more details.
+
 ros2cli
 ^^^^^^^