Fixes #476

The parameter substeps in the Simulation config had no influence on the
rendering frequency.
Additionally, app.update was not properly called when initializing the
stage due to the render method overload. This led to problems when
modifying the render interval.

- Merged physics stepping and rendering inside the step method in the
simulation config.
- Renamed substeps to render_interval in the simulation config.
- Updated all the tasks

## Type of change

- Breaking change (fix or feature that would cause existing
functionality to not work as expected)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] 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 run all the tests with `./isaaclab.sh --test` and they pass
- [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