Navigator: Use maximum flight altitude to limit missions

This change limits all mission items to the maximum flight altitude. The mission will still be executed and flown,
but the vehicle will never exceed the mission altitude. This ensures the vehicle can always reach the mission
items. Wether or not the entire mission should be rejected if it falls outside of the fenced area is enforced
in the mission feasibility checker function.

src/modules/navigator/follow_target.cpp

@@ -361,6 +361,7 @@ void FollowTarget::update_position_sp(bool use_velocity, bool use_position, floa
 
 	pos_sp_triplet->previous.valid = use_position;
 	pos_sp_triplet->previous = pos_sp_triplet->current;
+	mission_apply_limitation(&_mission_item);
 	mission_item_to_position_setpoint(_mission_item, &pos_sp_triplet->current);
 	pos_sp_triplet->current.type = position_setpoint_s::SETPOINT_TYPE_FOLLOW_TARGET;
 	pos_sp_triplet->current.position_valid = use_position;