Adds typescript types & edits package.json to support it

[anglinb]

👋 Feel free to close this if you're not much of a typescript person. I'm planning on extending this project (in my fork) and I prefer my types so decided to offer the typed starting project back if that's helpful before I go messing with it. 🙂

• Adds tsconfig.json
• Changes all files from .js to .ts
• Changes package.json config for dev & build
• Bumps sharp to 0.30.1 to run on Node 16

I verified that the dev, build, & start commands work.

[anatolinicolae]

Looks great to me! Managed to deploy this PR on Railway.app as well, since main branch is currently failing.