fix(payment): PAYMENTS-11168 Update transaction created webhook order_id to be string (#1146)

<!-- Ticket number or summary of work -->
# [PAYMENTS-11168]


## What changed?
<!-- Provide a bulleted list in the present tense -->
* Updating the `order_id` field for the
`store/order/transaction/created` scope webhook event to be string.

### Testing
Performing a test in integration, we can see that the `order_id` is
actually returned as a string. So updating the docs to accurately
reflect this.
```
{
  "producer": "stores/ktvx0elrm2",
  "hash": "0c54b57ccda4fd93c28454242c862a9e8fd526f2",
  "created_at": 1762126619,
  "store_id": "16532817",
  "scope": "store/order/transaction/created",
  "data": {
    "order_id": "100",
    "transaction_id": "80047454917",
    "type": "transaction",
    "transaction_status": "complete",
    "transaction_type": "purchase",
    "result": {
      "code": "paid",
      "message": "Paid",
      "type": "success"
    },
    "platform_transaction_id": "5292709",
    "provider_transaction_id": "80047454917"
  }
}
```

## Release notes draft
<!-- Provide an entry for the release notes using simple, conversational
language. Don't be too technical. Explain how the change will benefit
the merchant and link to the feature.

Examples:
* The newly-released [X feature] is now available to use. Now, you’ll be
able to [perform Y action].
* We're happy to announce [X feature], which can help you [perform Y
action].
* [X feature] helps you to create [Y response] using the [Z query
parameter]. Now, you can deliver [ex, localized shopping experiences for
your customers].
* Fixed a bug in the [X endpoint]. Now the [Y field] will appear when
you click [Z option]. -->
* Fixed an error to update the `order_id` field for the
`store/order/transaction/created` scope webhook event to be string. This
now accurately reflects the type that is returned in the payload.

## Anything else?
<!-- Add related PRs, salient notes, additional ticket numbers, etc. -->

ping @bc-afeng 


[PAYMENTS-11168]:
https://bigcommercecloud.atlassian.net/browse/PAYMENTS-11168?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: bc-afeng

docs/integrations/webhooks/events/index.mdx

@@ -607,7 +607,7 @@ Payload objects with the following scopes take the form that follows:
   "store_id": "1025646",
   "data": {
     "type": "transaction", // will always be transaction
-    "order_id": 250, // ID of the order associated with the transaction
+    "order_id": "250", // ID of the order associated with the transaction
     "transaction_id": "176342342", // ID of the transaction; created by the payment provider
     "transaction_status": "complete",
     "transaction_type": "capture",

docs/webhooks/callbacks/store_order_transaction_created.yml

@@ -18,7 +18,7 @@ properties:
         type: object
         properties:
           order_id:
-            type: integer
+            type: string
           transaction_id:
             type: string
           type: