msg: Create message for GPS drift rates

This data is only updated at 5Hz and only required pre-flight.

msg/CMakeLists.txt

@@ -52,6 +52,7 @@ set(msg_files
 	distance_sensor.msg
 	ekf2_innovations.msg
 	ekf2_timestamps.msg
+	ekf_gps_drift.msg
 	ekf_gps_position.msg
 	esc_report.msg
 	esc_status.msg

msg/ekf_gps_drift.msg

@@ -0,0 +1,5 @@
+uint64 timestamp		# time since system start (microseconds)
+float32 hpos_drift_rate		# Horizontal position rate magnitude checked using EKF2_REQ_HDRIFT (m/s)
+float32 vpos_drift_rate		# Vertical position rate magnitude checked using EKF2_REQ_VDRIFT (m/s)
+float32 hspd			# Filtered horizontal velocity magnitude checked using EKF2_REQ_HDRIFT (m/s)
+bool blocked			# true when drift calculation is blocked due to IMU movement check controlled by EKF2_MOVE_TEST