feat: add LNBits wallet plugin integration

- Introduced LNBits as a Lightning Network wallet provider for Lamassu ATMs.
- Added configuration options for LNBits in the environment variables.
- Implemented core functionalities including invoice creation, payment processing, balance monitoring, and payment status tracking.
- Created unit tests for the LNBits plugin to ensure functionality and error handling.
- Updated development environment setup to include LNBits configuration.

packages/server/.sample.env

@@ -37,6 +37,12 @@ HOSTNAME=
 LOG_LEVEL=
 LIGHTNING_NETWORK_DAEMON=
 
+## LNBits Configuration (Lightning Network)
+# LNBits server URL (e.g., https://legend.lnbits.com)
+LNBITS_ENDPOINT=
+# Admin key for the LNBits wallet (wallet-specific, no separate walletId needed)
+LNBITS_ADMIN_KEY=
+
 # Crypto nodes related variables
 
 ## Location info (can be local or remote)