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`
{
    if (!ParserKeyword{"SYSTEM"}.ignore(pos, expected))
        return false;
    using Type = ASTSystemQuery::Type;
    auto res = std::make_shared<ASTSystemQuery>();
    bool found = false;
    for (int i = static_cast<int>(Type::UNKNOWN) + 1; i < static_cast<int>(Type::END); ++i)
    {
        Type t = static_cast<Type>(i);
        if (ParserKeyword{ASTSystemQuery::typeToString(t)}.ignore(pos, expected))
        {
            res->type = t;
            found = true;
        }
    }
    if (!found)
        return false;
    switch (res->type)
    {
        case Type::RELOAD_DICTIONARY:
        {
            String cluster_str;
            if (ParserKeyword{"ON"}.ignore(pos, expected))
            {
                if (!ASTQueryWithOnCluster::parse(pos, cluster_str, expected))
                    return false;