- handle saving the mag bias per sensor (across all estimator instances using that mag) in sensors/vehicle_magnetometer
- this is now saving back to the actual mag calibration CAL_MAGn_OFF{X,Y,Z}
- ekf2 reset mag mag bias on any magnetometer or calibration change
- use Kalman filter scheme to update stored mag bias parameters using all available bias estimates for that sensor
Co-authored-by: Paul Riseborough <gncsolns@gmail.com>