Add default jpackage target

Currently, I get

```
Cannot locate tasks that match ':jabsrv-cli:jpackage' as task 'jpackage' is ambiguous in project ':jabsrv-cli'. Candidates are: 'jpackageMacos-13', 'jpackageMacos-14', 'jpackageUbuntu-22.04', 'jpackageWindows-2022'.
```

Since I don't want to give the tool the current operating system, since the tool should know where it runs.