Export configuration type

[regseb]

Export the types (file *.d.ts) of the configuration so that we can validate our configurations with TypeScript.

---

Example of npmpackagejsonlint.config.js if types are exported:

// @ts-check
/**
 * @type {import('npm-package-json-lint').Configuration}
 */
module.exports = {
  rules: {
    'require-author': 'error'
  }
};