passing customer login to checkout fix

[michenly]

WHY are these changes introduced?

A bug was found where the logged-in customer status is not passed to checkout. This is because the customer access token from Customer Account API cannot be passed to storefront API as buyer identify.

WHAT is this pull request doing?

In skeleton

• remove buyer identity cart functions
• pass logged_in =true query param to checkout link. Instructions from https://shopify.dev/docs/api/customer#step-stay-authenticated-on-checkout
• ensure session is committed after being clear
• add instruction to ensure the new customer experience is enable
• do all the above to demo-store & examples

HOW to test your changes?

1. link a shop to skeleton to use customer account api
2. login to customer account
3. add an product before or after the login
4. go to cart >> checkout
5. see customer information being pre-filled on the checkout page
6. logout on the checkout page
7. go back to the hydrogen site and click on Account
8. see the Account page redirecting you to shopify login page
9. go back to the hydrogen site and see the menu item is now "Login in" instead of "Account"

Post-merge steps

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[michenly]

Having this in the code feels really strange since it is only for development and only relevant if you are doing anything customer account related. Can I remove it?

[michenly]

Maybe we can make it so you put in the domain during npm run dev --ngrok-domain=accepted-shrimp-privately.ngrok-free.app

this will automatically start ngrok for you, do the domain change and change dev up message too.

it will mean that our shopify hydrogen dev will depend on ngrok. Lets discuss in a separate PR since its outside of the scope of the current task