Add LNURL-pay drain

[dangeross]

Calculate an invoice inversing the Boltz fees in a way to drain the wallet. If the invoice returned contains an MRH request a new invoice without Boltz fees.

Some findings

Calculating the inverse fee can be tricky. Every time the invoice amount goes from x000 to x001 (e.g 2000 -> 2001) the total amount skips a number. It means we could not create a drain tx for that amount (unless we hack the drain tx and increase the fee out by 1 sat)

Invoice Boltz Fee       Network Fee     Total
1000    1               14              1015
1001    2               14              1017

1999    2               14              2015
2000    2               14              2016
2001    3               14              2018
2002    3               14              2019

2999    3               14              3016
3000    3               14              3017
3001    4               14              3019
3002    4               14              3020

So if the wallet total is 2031 sats, lockup fee is 14 sats its not possible to create an invoice that will result in 2017 sats (invoice amount + boltz fee + network fee) for the drain

(again unless you change the lockup fee tx output to 15 sats in this case)

2031 total - 15 lockup fee = 2016
2016 - 14 network fee - 2 boltz fee = 2000

[ok300]

This is because the Boltz service fees use a ceil rounding in their calculation.

// For 1000 sats:
service_fee = ceil( amount * service_feerate )
            = ceil( 1000 * 0.001 )
            = 1

// For 1001 sats:
service_fee = ceil( 1001 * 0.001 )
            = ceil( 1.001 )
            = 2