Reorganize Fastify table of contents [WIP]

[Sambaboy]

changes... re-org TOC with new chapter titles add Terminology section with Fastify terms defined in Resources chapter

Checklist

• [ ] run npm run test and npm run benchmark
• [ ] tests and/or benchmarks are included
• [ ] documentation is changed or added
• [ ] commit message and code follows Code of conduct

[Sambaboy]

My PR was by no means intended as a straight merge into the Fastify's Docs master repo. It is merely guidelines to the docs' guru in rethinking how to organize.

[jsumners]

Feedback is of course welcome, but you'll find that it gets incorporated quicker (if at all) if you submit a PR that actually implements your ideas.

[Eomm]

Closing for https://github.com/fastify/website-next