Adds dataclass replacement for comand-line config overwrite

[Fisher-Wang]

Description

For example, I have a field robot in DirectEnvCfg with default value FRANKA_ISAACLAB_CFG

@configclass
class MyTaskEnvCfg(DirectRLEnvCfg):
    robot: ArticulationCfg = FRANKA_ISAACLAB_CFG

And FRANKA_ISAACLAB_CFG is defined as

@configclass
class FrankaIsaaclabCfg(ArticulationCfg):
    prim_path = "/World/envs/env_.*/Robot"
    spawn = sim_utils.UsdFileCfg(
    ...
FRANKA_ISAACLAB_CFG = FrankaIsaaclabCfg()

When I want to replace the robot config to another one, say FrankaWithGripperExtensionCfg, which is defined as

@configclass
class FrankaWithGripperExtensionCfg(ArticulationCfg):
    prim_path = "/World/envs/env_.*/Robot"
    spawn = sim_utils.UsdFileCfg(
    ...
FRANKA_WITH_GRIPPER_EXTENSION_CFG = FrankaIsaaclabCfg()

I can either run

python my_script.py env.robot=src.cfg.robot.franka:FRANKA_WITH_GRIPPER_EXTENSION_CFG <other_args>

or

python my_script.py env.robot=src.cfg.robot.franka:FrankaWithGripperExtensionCfg <other_args>

Currently I didn't find any support for this functionality in doc, so I implement a prototype, which is tested successfully in my own codebase.

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots

Run without env.robot=src.cfg.robot.franka:FrankaWithGripperExtensionCfg:

Run with env.robot=src.cfg.robot.franka:FrankaWithGripperExtensionCfg:

As you can see, the color of two arm is different, since I use two different configuration linked to different usd file.

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there