SIM: Set up gazebo with ros2 control

[nico-palmar]

Need to be able to control the drivetrain in gazebo.

We want to use the GazeboSystem ros2 control built in package to do this.

Right now, we have the issue that our actual rover uses a actuator interface to set up our motors, but the gazebo plugin is expecting a system interface. To fix this, we should:

1. Create a new macro to parameterize a joint in simulation (requires joint name, command interface, and two state interfaces).
2. Create another macro that calls the ros2 control with the gazebo system plugin, and calls the 5 joint plugins.
3. Use xml if/unless logic to check whether or not sim is running (if sim, use the actuator ros2 control tags, otherwise the new system tags).

Before we can merge stuff in, we probably want both real robot hardware and simulation to have the same launch file as an entry point, but just set sim:=true or sim:=false within the launch file depending on what we want. This is more so a matter of cleaning up the code and making it look nice (but important to keep a work-able codebase going).