Environment variables in paths are not expanded

### Expected Behavior

Environment variables in paths are not expanded

1. in `extra_model_paths.yaml`
`base_path: $DATA_PATH\models`

Should be expanded internally to whatever the environment variable $DATA_PATH references, with `os.path.expanduser(os.path.expandvars(...))`
(This is OS agnostic, because in python environment variables are always prefixed with $ no matter the OS)

2. The same issue also happens in command line args. e.g.
`python main.py --input-directory "$DATA_PATH\inputs"` is not expanded. However there is a work around for this by expanding before passing. E.g. `python main.py --input-directory "%DATA_PATH%\inputs"`. But there is no workaround for expanding the yaml contents.

### Actual Behavior

See above

### Steps to Reproduce

See above

### Debug Logs

```powershell
See above
```

### Other

_No response_