Better Resolution of djLspPath in VS Code settings

Please add support for resolving `${workspaceFolder}` in the `djangoTemplateLsp.djLspPath` setting.

Example use case:

```
"djangoTemplateLsp.djLspPath": "${workspaceFolder}/.venv/bin/djlsp"
```

This would allow projects with a local `.venv` to work without needing absolute paths.