Better support for anonymous orders [#3214820]

Problem/Motivation

Anonymous orders creates and loads customer with empty e-mail, so in Stripe there will be one customer for all anonymous orders. Also payments from anonymous orders can not receive receipts because order e-mail is not send to Stripe.

Steps to reproduce

Create anonymous orders.

Proposed resolution

Do not create nor load customer if order is anonymous. Also fill receipt_email in payment intent by order's e-mail.

Remaining tasks

Review my patch.

User interface changes

None.

API changes

None.

Data model changes

No change in Drupal, just on Stripe side - receipt_email filled in all payments and no customer profiles for anonymous orders.

Issue fork commerce_decoupled_stripe-3214820

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3214820-send-also-receiptemail changes, plain diff MR !2
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