Include jlpm within this package

[fcollonval]

We should add jlpm within this package rather than jupyterlab.

For now, jlpm define there: https://github.com/jupyterlab/jupyterlab/blob/main/jupyterlab/jlpmapp.py
with the entrypoint defined there: https://github.com/jupyterlab/jupyterlab/blob/e048f27548969c0e4403417ac04bc186f119128f/pyproject.toml#L60