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

**Use case**
People are used to Postgres.
#pragma once
#include <list>
#include <Parsers/IParserBase.h>
#include <Parsers/CommonParsers.h>
namespace DB
{
/** Consequent pairs of rows: the operator and the corresponding function. For example, "+" -> "plus".
  * The parsing order of the operators is significant.
  */
using Operators_t = const char **;
class ParserList : public IParserBase
{
public:
    ParserList(ParserPtr && elem_parser_, ParserPtr && separator_parser_, bool allow_empty_ = true, char result_separator_ = ',')