Allow using Inertia without a session

[m1guelpf]

This allows using Inertia for unauthenticated routes. I ran into this when moving the authentication scaffolding to Inertia, which I'll admit is outside the intended scope of the package, but still would be nice to have it working.

For anyone else running into this while this is open (or rejected), here's a hacky workaround

Add this function at the end of your app/Http/Kernel.php:

public function updateWebGroup(\Closure $closure)
{
    $this->middlewareGroups['web'] = $closure($this->middlewareGroups['web']) ?? $this->middlewareGroups['web'];

    $this->syncMiddlewareToRouter();
}

And this to the boot method of your JetstreamServiceProvider:

$this->app->make(Kernel::class)->updateWebGroup(function (array $web) {
    $web[array_search(\Laravel\Jetstream\Http\Middleware\ShareInertiaData::class, $web)] = \App\Http\Middleware\ShareInertiaData::class;

     return $web;
});

Now, copy the ShareInertiaData middleware to your local middleware folder and apply the changes of this PR.