Add a GET endpoint for customer identity and billing address

It looks like the Storefront API currently allows us to set and update a customer’s billing address, but there does not appear to be an endpoint for retrieving the currently stored address.

The sign-in and refresh responses only return the customer ID, name and email, and there is no documented GET endpoint for /api/customer/identity.

For a custom customer portal, it would be very useful to have an authenticated endpoint such as:

GET /api/customer/identity

returning the customer’s name, email, billing address and communication preferences.

Without this, we can update the billing address but cannot display or prefill the existing data.