Add helper command for getting Shopify-related checkout details

[notbakaneko]

Mainly to get the Shopify order orderNumber or id.
It calls the public Storefront API so it can use the same token instead of needed a separate oauth client/secret for the admin API.
API version is matched to the current shopify-buy sdk's version (and different version has different schema and I don't feel like updating it now)

[peppy]

Do you think it would be feasible to store these at some point in the checkout process to the database? This would allow for easier lookups from external tooling.

[notbakaneko]

That's part of the plan.
The current public token is also rate-limited by IP which normally isn't a problem during checkout since they're initiated from the user's end;

[nanaya]

Seems like a lot of things for what should be just storing order_number during the webhook callback or something 🤔 I guess it's useful for checking existing orders