Automate Install of python-lsp-server Dependencies

[ebresie]

Presently as pre-requisite step of Python4NB setup, it's necessary to have the Python-lsp server installed manually.

This task is to add functionality to install this in a more automated way which could be done

• on first usage with given default python, run a given "package install" command to install into the given environment.
• via some sort of "install server" button trigger to do so

[ebresie]

On python-lsp/python-lsp-server#283 discussion thread, it was suggested usage of a "pyproject-toml" might be usable.

Need to investigate further see https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/