commander: report GNSS yaw fault to user

src/modules/ekf2/EKF/common.h

@@ -487,6 +487,7 @@ union filter_control_status_u {
 		uint32_t ev_vel      : 1; ///< 24 - true when local frame velocity data fusion from external vision measurements is intended
 		uint32_t synthetic_mag_z : 1; ///< 25 - true when we are using a synthesized measurement for the magnetometer Z component
 		uint32_t vehicle_at_rest : 1; ///< 26 - true when the vehicle is at rest
+		uint32_t gps_yaw_fault : 1; ///< 27 - true when the GNSS heading has been declared faulty and is no longer being used
 	} flags;
 	uint32_t value;
 };