message: example: instantiate action plugin earlier
  If instantiated earlier, the action plugin can "prepare" and by the
  time it's used it will have received the landed state.
diff: @@ -49,6 +49,7 @@ int main(int /*argc*/, char ** /*argv*/)
  // dc.system(uint64_t uuid);
  System &system = dc.system();
  auto telemetry = std::make_shared<Telemetry>(system);
  + auto action = std::make_shared<Action>(system);
  // We want to listen to the altitude of the drone at 1 Hz.
  const Telemetry::Result set_rate_result = telemetry->set_rate_position(1.0);
  @@ -74,8 +75,6 @@ int main(int /*argc*/, char ** /*argv*/)
  return 1;
  }
  - auto action = std::make_shared<Action>(system);
  -
  // Arm vehicle
  std::cout << "Arming..." << std::endl;
  const ActionResult arm_result = action->arm();
  