feat: add support for load package via require()

[tugay-radity]

With Node.js's new experimental flag --experimental-require-module it is possible to require() ECMAScript modules into CommonJS. For more information, see the Node.js documentation.

However without having require added to the exports the cjs loader throws Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: No "exports" main defined in .../node_modules/@adminjs/nestjs/package.json

To resolve the issue, require path added to the package.json.