OpenApiMessages.proto: ProtoOATraderLogoutReq -> ProtoOAAccountLogoutReq

[raul-gherman]

documentation / comment for message ProtoOAAccountLogoutRes should be adjusted, as ProtoOATraderLogoutReq does not exist;
proposed value:

/** Response to the ProtoOAAccountLogoutReq request. Actual logout of trading account will be completed on ProtoOAAccountDisconnectEvent. */
message ProtoOAAccountLogoutRes {
    optional ProtoOAPayloadType payloadType = 1 [default = PROTO_OA_ACCOUNT_LOGOUT_RES];

    required int64 ctidTraderAccountId = 2; // The unique identifier of the trader's account in cTrader platform.
}