fix(ocpp20): send actual MeterValues on trigger and block sessions during firmware update
- F06.FR.06: TriggerMessage for MeterValues now sends TransactionEvent(Updated)
with actual meter readings for each EVSE with active transactions instead
of hardcoded value: 0
- L01.FR.07: UpdateFirmware sets idle EVSE connectors to Unavailable when
AllowNewSessionsPendingFirmwareUpdate is absent or false, preventing new
sessions while waiting for active transactions to end before installing