Adds friction force reporting to ContactSensor

[gattra-rai]

Description

This PR extends the ContactSensor class to expose aggregated friction forces for each filtered body. It uses the same vectorized approach used for contact_points.

Concretely, this change introduces:

• ContactSensorCfg.track_friction_forces toggle to turn on friction tracking
• ContactSensorData.friction_forces_w where the sum of friction forces for each filtered body are stored

Fixes https://github.com/isaac-sim/IsaacLab/issues/2074, #2064

Performance

Results of check_contact_sensor.py with track_friction_data = False:

avg dt real-time 0.017448579105403043
avg dt real-time 0.017589360827958443
avg dt real-time 0.016146250123070787

Results of check_contact_sensor.py with track_friction_data = True:

avg dt real-time 0.01818224351439858
avg dt real-time 0.017720674386015163
avg dt real-time 0.01777262271923246

Type of change

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

Checklist

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

[ooctipus]

I am curious how do you use the friction force for your learning setup, would love to learn how you guys are using it : ))

[Mayankm96]

@greptileai some help ;)

[Mayankm96]

@greptileai everything you said. Whatever it takes to improve the MR and make it less error-prone and feature complete :)

[gattra-rai]

Responding to greptile's suggestions:

1. Done
2. Won't do. This was an intentional design choice as friction forces can be zero if not in contact, whereas contact points cannot
3. Done
4. Done
5. Done

[kellyguo11]

@gattra-rai could you take a look at the doc build issues? https://github.com/isaac-sim/IsaacLab/actions/runs/19120652606/job/54640238296?pr=3563. perhaps some of the suggestions from greptile might help