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

**Use case**
People are used to Postgres.
{
private:
    static const char * operators[];
protected:
    const char * getName() const override { return "tuple element expression"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserUnaryMinusExpression : public IParserBase
{
private:
    static const char * operators[];
    ParserPrefixUnaryOperatorExpression operator_parser {operators, std::make_unique<ParserTupleElementExpression>()};
protected:
    const char * getName() const override { return "unary minus expression"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserMultiplicativeExpression : public IParserBase
{
private:
    static const char * operators[];
    ParserLeftAssociativeBinaryOperatorList operator_parser {operators, std::make_unique<ParserUnaryMinusExpression>()};
protected:
    const char * getName() const  override { return "multiplicative expression"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override
    {
        return operator_parser.parse(pos, node, expected);
    }
};
class ParserDateOperatorExpression : public IParserBase