Consider vendoring kjob and other binary dependencies

When I tried the latest `xpk` 0.8.0, it requires https://github.com/kubernetes-sigs/kjob/blob/main/docs/installation.md, which I'm not sure how to install.

I think the best user experience can be achieved by bundling the desired version of `kjob` and other dependencies inside the `xpk` release published to PyPI. This way I just need to `pip install xpk` and everything works.