Adds support for underactuated joints in Articulation

[Mayankm96]

Description

This MR adds support for articulation with underactuated and mimic joint systems.

It introduces the following changes:

1. The fields actuated_joints_names and mimic_joints_info to the articulation config.

2. The following fields to ArticulationData

   • actuated_joint_names and actuated_joint_indices
   • mimic_joint_names and mimic_joint_indices

3. Modifications inside the articulation class to update joint targets, joint states, and default joint states by providing only the actuated joint values and inferring the underactuated ones.

Fixes # (issue)

Type of change

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

Screenshots

Please attach before and after screenshots of the change if applicable.

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