Add missing collision approximation choices

# Description

Add some missing collision approximation options in convert_mesh.py
file. Some collision approximation options were missing in the code, but
the MeshConverterCfg class has them as possible options


https://github.com/isaac-sim/IsaacLab/blob/21173c3e933a9236d6eb5eb2adb903494ba9a418/source/standalone/tools/convert_mesh.py#L60


https://github.com/isaac-sim/IsaacLab/blob/21173c3e933a9236d6eb5eb2adb903494ba9a418/source/extensions/omni.isaac.lab/omni/isaac/lab/sim/converters/mesh_converter_cfg.py#L39-L41

Fixes https://github.com/isaac-sim/IsaacLab/issues/1713#issue-2807158637


## Type of change

- New feature (non-breaking change which adds functionality)

## Checklist

- [ ] 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
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

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Signed-off-by: Virgilio Gomez Lambo <82644963+virgilio96upm@users.noreply.github.com>