Allow payment_intent_succeeded webhook to handle orders without intent_id attached

[daquinons]

Fixes 1202-gh-Automattic/woocommerce-payments-server

Changes proposed in this Pull Request

There has been a lot of reports in different merchants about a situation where an order was successfully paid in Stripe side, but canceled in WooCommerce (because of woocommerce_hold_stock_minutes).

Find more about it and its investigation in the shared links here 1202-gh-Automattic/woocommerce-payments-server

This PR allows the webhook to obtain an order using the attached order_id in the metadata of the object, in case the intent_id was not properly attached into the order because of any racing condition.

@dmallory42 has also contributed moving attach_intent_info_to_order and attach_exchange_info_to_order higher in the execution to try to mitigate the racing condition as we spoke here p1634210077172300-slack-C0208C3BXHP

Testing instructions

• Run the tests, I've added a new one that gets an order when one is not found using intent_id.
• To test it manually, go to this line

  woocommerce-payments/includes/admin/class-wc-rest-payments-webhook-controller.php

  Line 264 in 38dade9

  $order = $this->wcpay_db->order_from_intent_id( $intent_id );

  and change it for
  $order = $this->wcpay_db->order_from_intent_id( "anything" ); in order to simulate getting an intent_id that we had no record of.
• Make a purchase
• See in the logs intent_id not found, using order_id to retrieve order, that indicates the webhook has gone into the new added logic.
• Check the order is successfully marked as payment_complete after the order was successfully retrieved using the webhook metadata.

---

• Added changelog entry (or does not apply)
• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Post merge

• Added testing instructions to the release testing doc (or does not apply) here https://github.com/Automattic/woocommerce-payments/wiki/Release-testing-instructions-for-WC-Payments-3.2.0#fix-problem-where-an-order-gets-canceled-being-paid-properly-in-stripe

[dmallory42]

LGTM and works well, thanks for working on this!

As mentioned via Slack, I think we should add a few GlobalStep flows to the next release for using the checkout and the blocks checkout purchasing a simple product, subscription product, etc.