Adds option to define the concatenation dimension in the `ObservationManager` and change counter update in `CommandManager` (#2393)

# Description


Added support for concatenation of observations along different
dimensions in `ObservationManager`.

Updates the position where the command counter is increased to allow
checking for reset environments in the resample call of the
`CommandManager`

## Type of change

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

## 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 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: Pascal Roth <57946385+pascal-roth@users.noreply.github.com>
Signed-off-by: Kelly Guo <kellyg@nvidia.com>
Signed-off-by: Kelly Guo <kellyguo123@hotmail.com>
Co-authored-by: Mayank Mittal <12863862+Mayankm96@users.noreply.github.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>