Add @bind directive as a GraphQL analogue for Laravel's Route Model Binding

[remipelhate]

• Added or updated tests
• Documented user facing changes
• Updated CHANGELOG.md

Changes

This PR aims to bring (in my opinion) one of Laravel's most convenient features to Lighthouse's resolver system: Route Model Binding.

The code is based on an implementation I did a couple of months ago for a different project and as it has been really useful, I thought it maybe could be useful for others as well.

The general idea is to allow developers to define bindings for resolver arguments through the schema using a new @bind directive, which resolves a scalar identifier to an (Eloquent) model instance:

type Mutation {
    addUserToCompany(
        user: ID! @bind(class: "App\\Models\\User")
        company: ID! @bind(class: "App\\Models\\Company")
    ): Boolean!
}

These bindings are resolved before the query or mutation resolver is invoked, meaning that we have the instances available in the resolver without having to query for it in the resolver itself:

<?php

namespace App\Http\GraphQL\Mutations;

class AddUserToCompany
{
    /**
     * @param array{user: \App\Models\User, company: \App\Models\Company} $args
     */
    public function __invoke(mixed $root, array $args): bool
    {
        return $args['user']->associate($args['company'])->save();
    }
}

I added more examples and usages to the docs. Let me know if you think this would be a good addition to Lighthouse ;)

Breaking changes

This PR does not introduce any breaking changes.

[remipelhate]

Sorry for the many added lines, but at least most of them are coming from test cases.

[spawnia]

I like the concept!

[spawnia]

Released with https://github.com/nuwave/lighthouse/releases/tag/v6.48.0.