Add option to fetch after navigating

[ozziexsh]

Right now we fetch the page props before finishing the navigation on the vue-router side so that your page is loaded with the props ready to go

It'd be cool if we had a config which allowed you to fetch after navigating instead so that pages load instantly and you can show loading spinners or whatever until the props are ready

We'd need to also update the generated types to indicate that they are null to start out and not available yet