Send Payjoin #83
Description
I want to buy more Passport devices with my Passport on the Foundation BTCPay store using payjoin from Envoy.
Based on a similar PR in DIBA, a wasm wallet, this should be around a 250 line change using the payjoin crate including tests.
I guess this change may also require additional bip21 parsing with dart, though the payjoin crate includes it.