PIN Limit - LUD-21 (or whatever number it has when merged)

[X-Hades-X]

I implemented the pinLimit for LNBits since I host the boltcard for me and friends there. Some of them actually just refuse to have a boltcard if they can't have a pin. And others ask for this feature too
#21
(Implementing this probably next lnbits/tpos#16)

Implemented according to the not yet merged LUD here
https://github.com/bitcoin-ring/luds/blob/withdraw-pin/21.md
(according to LNURL Telegram some fiat converstion stuff is more important then this, but what do I know)

• optional 4 digit PIN can be set in LNBits Boltcards UI
• PIN is saved as clear text in DB (like k values; you've got other issues then a clear text 4 digit pin with this system)
• After 3rd wrong attempt card gets disabled; user has to enable the card over the LNBits Boltcards UI
• A correct attempt or enabling the card resets the pin_try counter

Have fun with it. I hope the LUD gets merged some day.