Allow publishing the schema and config seperately (#419)

Just tested this in a local project, everything works as before. This gives the option to

php artisan vendor:publish --provider="Nuwave\Lighthouse\Providers\LighthouseServiceProvider" --tag=schema

or

php artisan vendor:publish --provider="Nuwave\Lighthouse\Providers\LighthouseServiceProvider" --tag=config

to publish only the parts of the assets that you want