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Update GR1 pick place env with the following:

- Increase sim dt to 120 Hz for better physics stability during teleop
- Fix z position of object initial position so that it is not
penetrating table
- Update documentation for pick place Mimic demo

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- Bug fix (non-breaking change which fixes an issue)
- This change requires a documentation update

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