navigator: publish navigator mission item changes for logging

- new msg navigator_mission_item for inspecting navigator mission item processing

src/modules/logger/logged_topics.cpp

@@ -70,6 +70,7 @@ void LoggedTopics::add_default_topics()
 	add_topic("manual_control_setpoint", 200);
 	add_topic("mission");
 	add_topic("mission_result");
+	add_topic("navigator_mission_item");
 	add_topic("offboard_control_mode", 100);
 	add_topic("onboard_computer_status", 10);
 	add_topic("position_controller_status", 500);