Support DC_Core for NACS

[uhi22]

Start of the discussion was here: https://iso15118.elaad.io/pt2/15118-2/user-group/-/issues/42

"The NACS Spec is referencing the DIN SPEC 70121 for digital communication. In DIN SPEC 70121 Ed.3 the definition of the EnergyTransferMode "DC_core" will be modified in such a way that the reference to IEC 62196-2 will be removed to enable a use of this EnergyTransferMode for NACS."

This means, for use with NACS, we need in pev_sendChargeParameterDiscoveryReq() set the dinDocEnc.V2G_Message.Body.ChargeParameterDiscoveryReq.EVRequestedEnergyTransferType to DC_Core. To select between both options (CCS Type 1 and CCS Type 2 on the one side, and NACS on the other side) we need a configuration parameter.