Fix control testing sim input : change steer-rate to steer

Description

Change the input for controller_testing simulator. The simulator assumed that the input to the simulator is steering-rate, but it was actually steering.

The document says, the output of the control module is steering.

The input is fixed from steering-rate to steering in this MR.

(There was a discussion about this simulator input issue in #486 (closed))

With this MR, the controller tracking seems to get better (maybe because the model discrepancy between controller and simulator are solved).

Before :

After :

Note : When I run the simulation with the following command, the result differs with real_time_sim arg.

 ros2 launch controller_testing controller_testing_node.launch.py real_time_sim:=True with_rviz:=True

The following picture is the result when I run with real_time_sim:=False with this MR being merged.

Notes for Reviewer

The current MPC implementation assumes the base_link (the control point) is the center of the rear-wheels. Some document says the base_link is CoM. Which is correct? I need to confirm it. (added to the checklists below.)

Checklist

• Check the baseline definition (and fix the angular velocity calculation).
• Fix some plots (they are disabled for now)
• Documentation was updated

After these checklists are done, remove the WIP.