Ability to configure defaults in createInertiaApp()

[pascalbaljet]

Definitely WIP, but I'm already opening this to gather feedback/input.

This PR introduces a new defaults key to the CreateInertiaAppProps interface, allowing you to define application-wide defaults.

For example, you can use it to change the default queryStringArrayFormat from brackets to indices, or to attach default headers to every request:

createInertiaApp({
  title: (title) => `${title} - ${appName}`,

  // ...resolve, setup, progress, etc...

  defaults: {
    visitOptions: (href, options) => {
      return {
        queryStringArrayFormat: 'indices',
        headers: {
          'X-Foo': 'bar',
        },
      }
    },
  },
})

I've chosen to nest visitOptions under defaults so we don't bloat CreateInertiaAppProps if we end up adding more of these callbacks later on.

[pascalbaljet]

I've revisited this idea and it might be cool to follow Laravel's bootstrap/app.php approach:

createInertiaApp({
  resolve: (name) => resolvePageComponent(`./pages/${name}.vue`, import.meta.glob('./pages/**/*.vue')),
  setup({ el, App, props, plugin }) {
    createApp({ render: () => h(App, props) })
      .use(plugin)
      .use(ZiggyVue)
      .mount(el)
  },
})
  .withVisits((href, options) => ({
    queryStringArrayFormat: 'indices',
    headers: {
      'X-Custom-Header': 'CustomValue',
    },
  }))
  .withPrefetch({
    cache: '45s',
  })
  .withProgress({
    delay: 500,
    color: '#ff0000',
  })

We could also provide a config() helper to retrieve and set config values:

import { config } from '@inertiajs/vue3'

const allConfig = config()
const color = config('progress.color')

// Set single values with dot notation
config('progress.delay', 300)

// Set multiple values at once
config({
  progress: { delay: 250, color: '#29d' },
})

[pascalbaljet]

I'm closing this one in favor of other plans.

[pascalbaljet]

New PR: #2655