`INTERVAL '1 hour'` should be equivalent to `INTERVAL 1 HOUR`

**Use case**
People are used to Postgres.
else
    {
        auto old_pos = pos;
        auto maybe_an_subquery = pos->type == TokenType::OpeningRoundBracket;
        if (select.parse(pos, query, expected))
        {
            auto & select_ast = query->as<ASTSelectWithUnionQuery &>();
            if (select_ast.list_of_selects->children.size() == 1 && maybe_an_subquery)
            {
                
                pos = old_pos;
            }
            else
            {
                if (pos->type != TokenType::ClosingRoundBracket)
                    return false;
                ++pos;
                auto function_node = std::make_shared<ASTFunction>();
                tryGetIdentifierNameInto(identifier, function_node->name);
                auto expr_list_with_single_query = std::make_shared<ASTExpressionList>();
                expr_list_with_single_query->children.push_back(query);
                function_node->arguments = expr_list_with_single_query;
                function_node->children.push_back(function_node->arguments);
                node = function_node;
                return true;
            }
        }
    }
    const char * contents_begin = pos->begin;
    if (!contents.parse(pos, expr_list_args, expected))