The documentation of Cleo is heavily outdated and requires some work. This issue will be the place to track PRs addressing points from the following checklist:

• Update sphinx, build system files, and clean up config files.
• Setup CI job to build Sphinx documentation on change in the docs/ directory
• Update documentation content:
  • Update guides for common use cases
  • Add or update doc comments in public API code
  • Emphasize supported environment variables (see [DOC]: Document Environment Variables #363)
• Setup CI job with cron for the deployment of docs from main branch and latest stable version