Add MDB ESP32 Cashless project

This is an open-source project dedicated to implementing the MDB (Multi-Drop Bus) protocol for cashless vending machines, using ESP32 as the main platform and KiCad for PCB design. The MDB protocol is widely used in vending machines for communication between devices, enabling integration with cashless payment systems. The system also supports receiving credits over MQTT or Bluetooth, allowing integration with mobile apps, web backends, or other IoT platforms.