Migrates Soopervisor's doc to Jupyter Book.

[RodolfoFerro]

Describe your changes

Migrates Soopervisor's doc to Jupyter Book.

Contributes to #109

Comments:

• Testing doc builds at ReadTheDocs–rdt (with the dev branch) the builds were failing: https://readthedocs.org/projects/soopervisor/builds/18366224/
• Even if there were no errors, builds were failing because a config parameter in fail_on_warning, so I left it as false (https://github.com/ploomber/soopervisor/blob/52df3f56dc0b3dc977f4f1e7c3aeba8c2b306f0e/doc/_config.yml#L36) and it solved the problem: https://readthedocs.org/projects/soopervisor/builds/18366335/
• There will be warnings since some files from docs ara still incomplete and they're not referenced in toctree.
• Once it was tested from dev branch, the builds (@ rtd) have been set back to master branch.

A sample of the output hosted at rtd:

Checklist before requesting a review

• [x] I have performed a self-review of my code
• [x] I have added thorough tests (when necessary).
• [x] I have added the right documentation (when needed). Product update? If yes, write one line about this update.

[RodolfoFerro]

If for any reason after merging this PR (of course, after the rtd build) the docs still look with the older format, refresh the page clearing cache (cmd + shift + r or ctrl + shift + r)

[edublancas]

🎉