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

**Use case**
People are used to Postgres.
for (jt = operators; *jt; jt += 2)
                if (parseOperator(pos, *jt, expected))
                    break;
            if (!*jt)
                break;
            even = !even;
        }
        if (even)
            it = jt;    
    }
    ASTPtr elem;
    if (!elem_parser->parse(pos, elem, expected))
        return false;
    if (!*it)
        node = elem;
    else
    {
        
        auto function = std::make_shared<ASTFunction>();
        
        auto exp_list = std::make_shared<ASTExpressionList>();
        function->name = it[1];
        function->arguments = exp_list;
        function->children.push_back(exp_list);
        exp_list->children.push_back(elem);
        node = function;
    }
    return true;
}
bool ParserUnaryMinusExpression::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)