Add a command that will freeze clickhouse-server process with STOP signal and wakeup it after specified amount of time.
This is needed for testing (fault injection).

Wakeup can be done with `ShellCommand` running `sleep N && kill -CONT pid`
return "STOP TTL MERGES";
        case Type::START_TTL_MERGES:
            return "START TTL MERGES";
        case Type::STOP_MOVES:
            return "STOP MOVES";
        case Type::START_MOVES:
            return "START MOVES";
        case Type::STOP_FETCHES:
            return "STOP FETCHES";
        case Type::START_FETCHES:
            return "START FETCHES";
        case Type::STOP_REPLICATED_SENDS:
            return "STOP REPLICATED SENDS";
        case Type::START_REPLICATED_SENDS:
            return "START REPLICATED SENDS";
        case Type::STOP_REPLICATION_QUEUES:
            return "STOP REPLICATION QUEUES";
        case Type::START_REPLICATION_QUEUES:
            return "START REPLICATION QUEUES";
        case Type::STOP_DISTRIBUTED_SENDS:
            return "STOP DISTRIBUTED SENDS";
        case Type::START_DISTRIBUTED_SENDS:
            return "START DISTRIBUTED SENDS";
        case Type::FLUSH_LOGS:
            return "FLUSH LOGS";
        default:
            throw Exception("Unknown SYSTEM query command", ErrorCodes::LOGICAL_ERROR);
    }
}
void ASTSystemQuery::formatImpl(const FormatSettings & settings, FormatState &, FormatStateStacked) const