Stabilize Franka cloth rendering tests (isaac-sim#6563)

# Description

- Step the cloth test once (instead of 15 times earlier) before capture
to reduce solver nondeterminism
- Replace hard-coded physics-backend skips with a procedural check
against each env cfg's declared physics presets
- Refresh Newton golden images, and remove PhysX golden images for an
env that only supports Newton
- Disable instancing for Franka cloth/soft envs for all AOVs if the
render backend is IsaacSim RTX

## Type of change

- Test improvement

## Checklist

- [x] I have read and understood the [contribution
guidelines](https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html)
- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) 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

Author: huidongc

source/isaaclab_tasks/changelog.d/stabilize-deformable-rendering-test.skip

@@ -0,0 +1,4 @@
+Test-only: stabilized Franka cloth rendering tests by skipping unsupported physics presets
+procedurally, reducing the pre-capture simulation step to one, refreshing Newton golden images,
+and removing PhysX golden images for an env that only declares a Newton preset. No user-facing API
+change.