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

**Use case**
People are used to Postgres.
{
public:
    ParserExpressionList(bool allow_alias_without_as_keyword_)
        : allow_alias_without_as_keyword(allow_alias_without_as_keyword_) {}
protected:
    bool allow_alias_without_as_keyword;
    const char * getName() const override { return "list of expressions"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserNotEmptyExpressionList : public IParserBase
{
public:
    ParserNotEmptyExpressionList(bool allow_alias_without_as_keyword)
        : nested_parser(allow_alias_without_as_keyword) {}
private:
    ParserExpressionList nested_parser;
protected:
    const char * getName() const override { return "not empty list of expressions"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserOrderByExpressionList : public IParserBase