fw att ctrl: log the yaw rate command controlled by the wheel

msg/vehicle_rates_setpoint.msg

@@ -1,8 +1,12 @@
 uint64 timestamp	# time since system start (microseconds)
 
-float32 roll		# body angular rates in NED frame
-float32 pitch		# body angular rates in NED frame
-float32 yaw		# body angular rates in NED frame
+# body angular rates in NED frame
+float32 roll		# [rad/s] roll rate setpoint
+float32 pitch		# [rad/s] pitch rate setpoint
+float32 yaw		# [rad/s] yaw rate setpoint
+
+# [rad/s] yaw rate setpoint the wheel attempts to track (the wheel controller has different gains than the yaw controller)
+float32 yaw_via_wheel
 
 # For clarification: For multicopters thrust_body[0] and thrust[1] are usually 0 and thrust[2] is the negative throttle demand.
 # For fixed wings thrust_x is the throttle demand and thrust_y, thrust_z will usually be zero.