XR rendering requires DLSS RR to reduce the noise of visualization. This
PR:
-Adds xr rendering mode.
-Makes xr rendering mode the default unless explicitly set if xr is
enabled

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- Bug fix (non-breaking change which fixes an issue)

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- [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

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