Add backward compatibility with REST-style webhook topics (e.g. "orders/create")

[squatto]

v17 requires webhooks to be configured with GraphQL-style webhook topics (e.g. "ORDERS_CREATE") instead of the previously-used REST-style webhook topics (e.g. "orders/create"). If there are webhooks in the config and topic isn't changed on all of them during the upgrade process, an exception is thrown that it isn't terribly clear how to fix: Variable $topic of type WebhookSubscriptionTopic! was provided invalid value.

This PR adds backward compatibility with REST-style webhook topics through the use of a new utility method: Util::getGraphQLWebhookTopic(string $topic): string

Util::getGraphQLWebhookTopic('orders/created') === 'ORDERS_CREATED'

When the webhooks in the config are being created on the store, the topic is run through this method to ensure that the GraphQL-style topic is being used, even if the topic in the config is REST style.

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I also updated the shopify-app:make:webhook command output to include the GraphQL-style topic and the actual webhook handler URL (instead of a generic URL). For example:

$ php artisan shopify-app:make:webhook OrdersCreate orders/create
For non-GDPR webhooks, don't forget to register the webhook in config/shopify-app.php. Example:

    'webhooks' => [
        [
            'topic' => 'ORDERS_CREATE',
            'address' => 'https://shopifyapptest.ngrok.io/webhook/orders-create'
        ]
    ]

[squatto]

Thanks @osiset! 👍🏻