refactor(ocpp20): prefix FirmwareStatusEnumType, extend FirmwareStatus union

refactor(ocpp20): prefix FirmwareStatusEnumType, extend FirmwareStatus union

- Rename FirmwareStatusEnumType → OCPP20FirmwareStatusEnumType per
  existing OCPP16FirmwareStatus naming convention
- Extend FirmwareStatus union to include all OCPP 2.0.1 firmware states
- Extend FirmwareStatusNotificationRequest to union both versions
- Write firmwareStatus to stationInfo in sendFirmwareStatusNotification
  fixing hasFirmwareUpdateInProgress which was always returning false
- Stack-specific code uses OCPP20FirmwareStatusEnumType, common code
  uses generic FirmwareStatus union