create new mag_bias_estimator module

Co-authored-by: Daniel Agar <daniel@agar.ca>

msg/CMakeLists.txt

@@ -98,6 +98,7 @@ set(msg_files
 	log_message.msg
 	logger_status.msg
 	mag_worker_data.msg
+	magnetometer_bias_estimate.msg
 	manual_control_setpoint.msg
 	manual_control_switches.msg
 	mavlink_log.msg

msg/magnetometer_bias_estimate.msg

@@ -0,0 +1,7 @@
+uint64 timestamp                # time since system start (microseconds)
+
+float32[4] bias_x		# estimated X-bias of all the sensors
+float32[4] bias_y		# estimated Y-bias of all the sensors
+float32[4] bias_z		# estimated Z-bias of all the sensors
+
+bool[4] valid			# true if the estimator has converged