fixes #1295

• NWC new methods
• new hold_invoice_accepted notification
• LND implementation
• LDK implementation
• handle self-payments -> feat: add support for self payments for hold invoices #1304
• Add hold invoice support to JS SDK (@rolznz to do) -> feat: add hold invoice NWC methods and notification type js-sdk#382
• Draft NIP-47 spec PR -> NIP-47 Add Hold Invoice Support nostr-protocol/nips#1913
• expiry does not need to be mandatory any more in the spec (add more documentation regarding the expiry field, so that it's more obvious to the developer that it will not guarantee the receiver to be able to settle the invoice and that it should check the deadline timestamp in the notification.)
• return claim deadline for LDK and LND + documentation about why it's in blocks
• review if we need to lower the inactive background sync time for LDK (currently 1h) if it could cause issues with hold invoices having a shorter than expected claim deadline - update: I think it's ok for now