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