ESM updates

[dphiffer]

This PR attempts to bring the project up to speed with modern node.js:

1. Updates packages to use ESM style import and export rather than require() and module.exports (forced in part because dependency parse-favicon refused to work using CommonJS).
2. Replaces deprecated request package with calls to native fetch().
3. Updates other packages to latest versions.
4. Adds an .nvmrc to nudge users toward node.js LTS v20.
5. Updates package.json engines to v18.0.0 in order to get fetch() without needing to pass an experimental argument.
6. Switches config.json to config.js to make it work more easily with ESM imports.