Add standalone scripts to enable torchrl workflow

[fyu-bdai]

Description

Adds play.py and train.py scripts to train and evaluate policies with TorchRL. This PR is the second in a series of three to add torchrl as a new RL workflow to IsaacLab.

Related PRs:
#1178 : Adds required wrappers for TorchRL. This PR must be merged after #1178.

Fixes #1181

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

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