Feature: pull request reviews and comments

Hi there! I saw your [presentation at Boston Python](https://www.meetup.com/bostonpython/events/271887195). I'm already a light user of Datasette (thank you!), but wasn't aware of this project.

I've been working on a "pull request dashboard" to get a comprehensive view of the state of open PR's, esp. related to reviews (i.e., pending, approved, changes requested). Currently it's a CLI command, but I thought a Datasette UI might be fun.

I see that PR's are available from the `issues` command, but I don't see reviews anywhere. From the [API docs](https://docs.github.com/en/rest/reference/pulls#reviews), it looks like there are separate endpoints for those (as well as pull requests in general). What do you think about adding that? Would you accept a PR? Any sense of the level of effort?

Commencez par la commande `issues` existante et par la documentation liée de la GitHub REST API concernant les reviews de pull requests. Retracez la manière dont les données des pull requests sont actuellement enregistrées dans SQLite, puis définissez le périmètre des reviews et des commentaires. L'implémentation doit fournir les données demandées sur les reviews et les commentaires des pull requests via la commande existante du projet et la sortie de la base de données.

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