fix: Fixed possible memory violation after remove_node

[jmachowinski]

Up until this change, after the call to remove node, entities of a node might still be in the use by the executor. Therefore direct deletion of the node after the call might result in a memory violation if an entity would do a callback into the node itself. From now on, by default the remove_node will be blocking until all entities are released by the executor, which should be the expected behavior for most users.

This commit fixes https://github.com/ros2/rclcpp/issues/2749