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

**Use case**
People are used to Postgres.
{
private:
    ParserLogicalOrExpression elem_parser;
protected:
    const char * getName() const override { return "expression with ternary operator"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
class ParserLambdaExpression : public IParserBase
{
private:
    ParserTernaryOperatorExpression elem_parser;
protected:
    const char * getName() const override { return "lambda expression"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override;
};
using ParserExpression = ParserLambdaExpression;
class ParserExpressionWithOptionalAlias : public IParserBase
{
public:
    ParserExpressionWithOptionalAlias(bool allow_alias_without_as_keyword);
protected:
    ParserPtr impl;
    const char * getName() const override { return "expression with optional alias"; }
    bool parseImpl(Pos & pos, ASTPtr & node, Expected & expected) override
    {
        return impl->parse(pos, node, expected);
    }
};
class ParserExpressionList : public IParserBase