Add support for AssignedFulfillmentOrder resource

[Spotnyk]

This pull request supports the AssignedFulfillmentOrder resource:
https://shopify.dev/docs/api/admin-rest/2023-04/resources/assignedfulfillmentorder

AssignedFulfillmentOrder Resource

Example:

// Requesting all assigned fulfillment orders
$shopify->AssignedFulfillmentOrder()->get();

// Requesting assigned fulfillment orders (by status)
$shopify->AssignedFulfillmentOrder()->get(["assignment_status" => "fulfillment_requested"]);

// Requesting assigned fulfillment orders (by locations)
$shopify->AssignedFulfillmentOrder()->get(["location_ids" => ["123456789"]]);