Fix the release workflow

[brichet]

This PR adds a script to bump version, inspired from jupyter-collaboration. This script uses lerna to bump (as before), but also bump the root package.json manually.

__ATTEMPT 1: __ This PR remove the version from the root package.json and use the version from lerna.json as the releaser reference version.
This solution avoid treating the root package.json a one of the sub-project: lerna/lerna#2879 (comment) This solution does not work with the releaser with try to run npm pack, which does not work if the version is not specified in package.json.

__ATTEMPT 2: __This PR add the root package.json in workspaces, but excludes the root package from Nx target: lerna/lerna#2879 (comment) With this solution the build-npm step after the bump-version step was broken, it seems that jupyterlab-collaborative-chat and jupyterlab-ws-chat were not build @jupyter/chat anymore (and still depends on it).