fix(ocpp2): build meter values payload in broadcast channel for OCPP 2.0.x

fix(ocpp2): build meter values payload in broadcast channel for OCPP 2.0.x

The OCPP 2.0 branch in handleMeterValues was passing the raw broadcast
channel payload through to requestHandler without constructing the
required evseId and meterValue fields. Build the payload using
buildMeterValue and resolve evseId from connectorId, matching the
pattern used by the OCPP 1.6 branch.