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

**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
