The logic for grid cloning in Isaac Sim GridCloner (func:
`get_clone_transforms()`) and in TerrainImporter.py (func:
`_compute_env_origins_grid()`) are different. Consequently, they give
inconsistent values.

This PR fixes the TerrainImporter by updating the logic of
`_compute_env_origins_grid()` to make it consistent with IsaacSim.

Fixes #287

- 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] 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 `./orbit.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

---------
Signed-off-by: Shafeef Omar <shafeef901@gmail.com>
Co-authored-by: Mayank Mittal <12863862+Mayankm96@users.noreply.github.com>