[Feature Request] Add ability to pay with a LN URL withdrawal qr code (or text)

[jacobburrell]

Background:

1. A client attempted to make a payment using a Bitcoin ATM.
2. She purchased Bitcoin from a General Bytes Bitcoin ATM, which provided a printout containing a QR code with an LNURL withdrawal.
3. She did not have a Bitcoin wallet and simply wanted to pay her BTCPay Server invoice via Invoice Ninja.

It would be beneficial if BTCPay Server could offer a scan option that attempts to pay the invoice either partially or fully (but not exceeding the invoice amount).

If the LN withdrawal amount is significantly larger than the invoice, the system should ideally reject the transaction or offer a mechanism to refund the excess to another address (e.g., back to the ATM for change through a separate transaction).

The ability to use LN withdrawal might also be highly dependent on the Lightning Network (LN) node in use. For example, integrations with services like Strike (which doesn't seem to support LN withdrawal) or Blink (which does) could vary in complexity.