Update to new API for hodl invoices for better UX with Alby extension

[MoritzKa]

Is your feature request related to a problem? Please describe. Currently, Alby does not close when you use it to pay a hodl invoice.

Describe the solution you'd like update webln.sendPayment to webln.sendPaymentAsync

Additional context full API documentation and demo to test: https://www.webln.guide/building-lightning-apps/webln-reference/webln.sendpaymentasync

[Reckless-Satoshi]

Hey @MoritzKa Thank you for putting this in our radar and thank you too for taking the time to improve UX for hodl invoices!