Add kd_tau to oven PID parameters

stm-firmware/include/reflow-controller/settings/settings.h

@@ -28,6 +28,7 @@ struct oven_pid_settings {
 	float kd;
 	float kp;
 	float ki;
+	float kd_tau;
 	float t_sample;
 	float max_integral;
 };