add support for LUD-19 for boltcards extension

[gorrdy]

LNURLw (withdrawRequest) that is returned by calling the link from bolt card now returns another field "payLink" as defined in LUD-19.

This allows compatible wallet to create e.g. refund or cashback to the card itself without need to create a separate invoice or managing another separate LNURLp or LN address.

[prusnak]

small style nits

[gorrdy]

applied some suggestion on code formatting. thanks @prusnak

[arbadacarbaYK]

LUD19 was about tap and top up. How is topping up handled now ? This needs a wiki entry.

[gorrdy]

LUD19 was about tap and top up. How is topping up handled now ? This needs a wiki entry.

I don't think the topping up is handled in LNbits anyhow. This PR just serves the payLink when tapping the bolt card. It depends on the wallet on the other side how it handles it.

In LNbits I would like a implementation in e.g. TPoS extension in LNbits. Also this extension (boltcards) could have some page that reads the NFC card withDraw link and if there is a payLink field, then show some dialog how many sats to top up. Not sure where this should be in UI.

[arbadacarbaYK]

LUD19 was about tap and top up. How is topping up handled now ? This needs a wiki entry.

I don't think the topping up is handled in LNbits anyhow. This PR just serves the payLink when tapping the bolt card. It depends on the wallet on the other side how it handles it.

In LNbits I would like a implementation in e.g. TPoS extension in LNbits. Also this extension (boltcards) could have some page that reads the NFC card withDraw link and if there is a payLink field, then show some dialog how many sats to top up. Not sure where this should be in UI.

yes because we are waiting on the end of the discussion in the nfc mafia group how we want it. In the desc is not the way, cause it cannot be interpreted by the devices.
Wouldve like to see the end of that first. So far only LUD21 changes for boltcard on tpos are near to ready.
Apart from that LUD17 predescribes lnurlp:// not lnurl as a pay-link.

There also is a status page for boltcards that tal just made that should show this paylink.

This is just half of the story and the documentation is not handled also. LUDs have to be brought in LNbits wide not only for one extension.