The current onnx exporter does not export the empirical normalization
layer. This MR adds the empirical normalization exporting to the JIT
and ONNX exporters for RSL-RL.

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

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] I have run all the tests with `./orbit.sh --test` and they pass
(some did timeout)
- [x] 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

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Co-authored-by: Mayank Mittal <mittalma@leggedrobotics.com>