Simulate the SBG's magnetometer

Feature Request

Feature Description

We want to simulate the magnetometer from the SBG because it will be used as an input to our EKF in the future.

Implementation Considerations

There is no magnetometer plugin from the gazebo_plugins package. We are thus taking the magnetometer plugin from hector_gazebo (we used their IMU plugin before migrating to ROS2, and they have a branch for their plugins working on ROS2 now). This also let's us extend the plugin in the future when we want to model sensor drift.