✨ feat: made chapter data dynamic with Docusaurus customFields

[JoshuaKGoldberg]

PR Checklist

• [x] Addresses an existing open issue: fixes #19; fixes #24
• [x] That issue was marked as accepting prs
• [x] Steps in CONTRIBUTING.md were taken

Overview

Reads files from disk in docusaurus.config.js to accumulate a big object of all the projects.