Add option to disable Inertia Modal

So, early on in my Inertia development I tried to make it that when a non-Inertia response comes back from the XHR request, it would automatically display that as the current page, instead of in a modal. However, this was not possible to get working properly, especially when it came to history management, despite both @adamwathan and my best efforts. We seriously spent a ton of time on this…and our determination was that it couldn’t be done.

That said, Inertia can totally work in an app that has some Inertia pages, and some server-side rendered pages. If you have pages in your app that are not Inertia pages, simply make those visits using normal links, and not using <inertia-link>. If you are making an Inertia request, you must return an Inertia response.

@jakedowns You can stick something along these lines in your app.js file, the preventDefault() will stop the modal opening and you can add whatever code you want before that.

Inertia.on('invalid', (event) => {
    alert('custom error handling')
    event.preventDefault()
})