Removes the flag disable_contact_processing from SimulationContext

[Mayankm96]

Description

The disable_contact_processing flag inside the SimulationContext causes confusion, as we were setting it to True in many environments, but it should be False since we want PhysX to report the contacts.

This MR changes the default behavior now. It is always disabled (i.e. no contact reporting), until a contact sensor is created. It makes sure that the performance isn't hampered in situations where the user doesn't want to create any contact sensors.

Fixes # (issue)

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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

[jtigue-bdai]

Looks like contact_sensor tests are failing