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 (!ASTQueryWithOnCluster::parse(pos, cluster_str, expected))
                    return false;
            }
            res->cluster = cluster_str;
            if (!parseDatabaseAndTableName(pos, expected, res->database, res->table))
            {
                
                
                if (res->type == Type::FLUSH_DISTRIBUTED)
                    return false;
            }
            break;
        }
        case Type::STOP_MERGES:
        case Type::START_MERGES:
        {
            String storage_policy_str;
            String volume_str;
            if (ParserKeyword{"ON VOLUME"}.ignore(pos, expected))
            {
                ASTPtr ast;
                if (ParserIdentifier{}.parse(pos, ast, expected))
                    storage_policy_str = ast->as<ASTIdentifier &>().name();
                else
                    return false;
                if (!ParserToken{TokenType::Dot}.ignore(pos, expected))
                    return false;
                if (ParserIdentifier{}.parse(pos, ast, expected))
                    volume_str = ast->as<ASTIdentifier &>().name();