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

**Use case**
People are used to Postgres.
return false;
        ++pos;
        if (!ParserExpression().parse(pos, offset_node, expected))
            return false;
        if (pos->type != TokenType::Comma)
            return false;
        ++pos;
        if (!ParserExpression().parse(pos, timestamp_node, expected))
            return false;
    }
    else
    {
        
        if (!ParserExpression().parse(pos, timestamp_node, expected))
            return false;
        if (pos->type != TokenType::Comma)
            return false;
        ++pos;
        if (!ParserKeyword("INTERVAL").ignore(pos, expected))
            return false;
        if (!ParserExpression().parse(pos, offset_node, expected))
            return false;
        if (!parseIntervalKind(pos, expected, interval_kind))
            return false;
    }
    if (pos->type != TokenType::ClosingRoundBracket)
        return false;
    ++pos;
    auto interval_expr_list_args = std::make_shared<ASTExpressionList>();
    interval_expr_list_args->children = {offset_node};