Persist payment metadata for pending inbound payments instead of using paymentStore

Inbound Bolt11 and Bolt12 payments that are pending should now be stored in `PaymentMetadataStore` rather than directly in `PaymentStore`.
Once the payment is completed (successful or failed), it is then moved to `PaymentStore`, and its status is updated in `PaymentMetadata`.
This change maintains backward compatibility with the previous behavior of storing all payment information directly in `PaymentStore`.

issue #425

Author: moisesPompilio