commander: remove low priority thread, run tasks in a worker thread on demand

- removes race conditions
- removes dependencies on static data & methods
- reduces RAM usage by ~3.8KB

src/modules/commander/Commander.hpp

@@ -36,6 +36,7 @@
 #include "Arming/PreFlightCheck/PreFlightCheck.hpp"
 #include "failure_detector/FailureDetector.hpp"
 #include "state_machine_helper.h"
+#include "worker_thread.hpp"
 
 #include <lib/controllib/blocks.hpp>
 #include <lib/hysteresis/hysteresis.h>
@@ -382,6 +383,8 @@ private:
 	safety_s		_safety{};
 	vtol_vehicle_status_s	_vtol_status{};
 
+	WorkerThread _worker_thread;
+
 	// Subscriptions
 	uORB::Subscription					_actuator_controls_sub{ORB_ID_VEHICLE_ATTITUDE_CONTROLS};
 	uORB::Subscription					_cmd_sub {ORB_ID(vehicle_command)};