Add checkoutToken api to unstable release

[dnagoda]

Background

Resolves https://github.com/Shopify/checkout-web/issues/22608

NOTE: I only included my changes. There's an issue with the current customer-account changes that blows up the build.

Solution

Provides stable id in checkout that can be mapped to WebPixel checkout payloads (via token in checkout payload) and Orders resource (via Admin REST API Orders checkout_token).

🎩

• Create a spin instance that includes the ui-extensions repo and checkout this branch: denii/unstable-release-2023-09-05
• Create a new app with checkout ui extension locally: yarn create @shopify/app and yarn generate extension
• In the local extension, use the new api, both directly and through the hook:

const { checkoutToken } = useApi();

const value = useSubscription(
  checkoutToken,
);

or

const hookValue = useCheckoutToken();

• In your app directory, run the following to copy the ui-extensions code into your app:

VM=direct.$(spin show -o fqdn)
rsync -av --delete $VM:~/src/github.com/Shopify/ui-extensions/packages/ui-extensions node_modules/@shopify/ && \
rsync -av --delete $VM:~/src/github.com/Shopify/ui-extensions/packages/ui-extensions-react node_modules/@shopify/

• Run yarn dev or yarn build to check that the app builds and can execute without error using the updated unstable api

Checklist

• I have 🎩'd these changes
• I have updated relevant documentation

[jamesvidler]

Nicely done 👍 Just a comment regarding the changeset description. Otherwise good to go.