feat: alternative initialize function

[innocenzi]

This PR adds an initializeProgress function which does the exact same thing as InertiaProgress#init, but with a syntax that is more in-line with the usual functional approach of JavaScript.

Basically, previously, you could do this:

import { createApp, h } from 'vue';
import { createInertiaApp } from '@inertiajs/inertia-vue3';
import { InertiaProgress } from '@inertiajs/progress';

createInertiaApp({
    resolve: (name: string) => import(`./pages/${name}`),
    setup: ({ el, app, props, plugin }) => createApp({ render: () => h(app, props) })
        .use(plugin)
        .mixin({ methods: { route } })
        .mount(el)
});

InertiaProgress.init({ color: '#4B5563' })

Now, you can do just like before, or do this:

import { createApp, h } from 'vue';
import { createInertiaApp } from '@inertiajs/inertia-vue3';
import { initializeProgress } from '@inertiajs/progress';

createInertiaApp({
    resolve: (name: string) => import(`./pages/${name}`),
    setup: ({ el, app, props, plugin }) => createApp({ render: () => h(app, props) })
        .use(plugin)
        .mixin({ methods: { route } })
        .mount(el)
});

initializeProgress({ color: '#4B5563' })

The typings have been updated as well. I'm not 100% sure of the name of initializeProgress. Other ideas:

• registerProgress
• makeProgress