adding wheeled files; TODO fix racetrack terrain C++ error

[geiko246]

Adds wheeled_gym files to GroundControl. A few standardization comments:

1. Put .usd asset files in omni.isac.groundcontrol_assets/data
2. train_rsl_rl.py saves runs to standalone/train/logs for lack of a better place
3. racetrack-terrain.usd for some reason causes this error:

  File "/home/tyler/Research/IsaacLab/source/extensions/omni.isaac.lab/omni/isaac/lab/sim/spawners/from_files/from_files.py", line 221, in _spawn_from_usd_file
    if not stage.ResolveIdentifierToEditTarget(usd_path):
Boost.Python.ArgumentError: Python argument types in
    Stage.ResolveIdentifierToEditTarget(Stage, tuple)
did not match C++ signature:
    ResolveIdentifierToEditTarget(pxrInternal_v0_22__pxrReserved__::UsdStage {lvalue}, std::string identifier)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/tyler/Research/GroundControl/source/standalone/train/train_rsl_rl.py", line 99, in <module>
    env = gym.make(args_cli.env_name, cfg=env_cfg, render_mode="rgb_array" if args_cli.video else None)
  File "/home/tyler/anaconda3/envs/GC/lib/python3.10/site-packages/gymnasium/envs/registration.py", line 814, in make
    raise type(e)(
Boost.Python.ArgumentError: Python argument types in
    Stage.ResolveIdentifierToEditTarget(Stage, tuple)
did not match C++ signature:
    ResolveIdentifierToEditTarget(pxrInternal_v0_22__pxrReserved__::UsdStage {lvalue}, std::string identifier) was raised from the environment creator for Isaac-MITCarRacetrack-v0 with kwargs 

Can test code by running:
python source/standalone/train/train_rsl_rl.py --headless --test-mode