Spike: Switch from lerna to pnpm workspaces

Personne n'a encore pris cette issue.

Our current lerna-based setup is very inefficient. Most of the pull requests in this repository are created by RenovateBot to update package-lock files, our git history is full of RenovateBot commits that make it difficult to spot relevant changes.

Let's investigate how to switch from lerna to [pnpm](https://pnpm.js.org/) and use a single root package-lock file for the entire monorepo.

References:
- pnpm workspaces: https://pnpm.js.org/en/workspaces
- Travis CI setup: https://pnpm.js.org/en/continuous-integration#travis

Topics to investigate:
- How to release new versions using conventional release process? Can we perhaps use https://github.com/atlassian/changesets? Related: https://github.com/pnpm/pnpm/issues/2225
- Does RenovateBot support pnpm? If not, is there any other bot we could use instead? E.g. GitHub's [Dependabot](https://github.com/dependabot). Related: https://github.com/renovatebot/renovate/issues/2015

Commencez par les références à pnpm workspaces et Travis CI dans l’issue, puis examinez les workflows actuels de Lerna, package-lock, RenovateBot et des releases. Le travail sera considéré comme terminé lorsqu’un plan de migration viable sera documenté, notamment la gestion des releases et la prise en charge des mises à jour de dépendances, plutôt que de modifier l’implémentation.

Rédigé par le modèle d'indexation à partir du texte de l'issue.