This change applies a new `create_new_stage` setting in Isaac Sim's
SimulationApp to avoid creating a default new stage on startup, which
introduces additional performance overhead.
Also fixes an error in hydra code when rebasing.

- Bug fix (non-breaking change which fixes an issue)
- New feature (non-breaking change which adds functionality)

- [ ] I have run the [`pre-commit` checks](https://pre-commit.com/) 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

<!--
As you go through the checklist above, you can mark something as done by
putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
-->

---------
Signed-off-by: peterd-NV <peterd@nvidia.com>
Co-authored-by: peterd-NV <peterd@nvidia.com>
Co-authored-by: CY Chen <cyc@nvidia.com>
Co-authored-by: oahmednv <oahmed@Nvidia.com>
Co-authored-by: Toni-SM <aserranomuno@nvidia.com>