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

**Use case**
People are used to Postgres.
auto exp_list = std::make_shared<ASTExpressionList>();
            ASTPtr elem;
            if (!(remaining_elem_parser ? remaining_elem_parser : first_elem_parser)->parse(pos, elem, expected))
                return false;
            
            function->name = it[1];
            function->arguments = exp_list;
            function->children.push_back(exp_list);
            exp_list->children.push_back(node);
            exp_list->children.push_back(elem);
            /** special exception for the access operator to the element of the array `x[y]`, which
              * contains the infix part '[' and the suffix ''] '(specified as' [')
              */
            if (0 == strcmp(it[0], "["))
            {
                if (pos->type != TokenType::ClosingSquareBracket)
                    return false;
                ++pos;
            }
            
            
            pos.increaseDepth();
            node = function;
        }
    }
    pos.depth = current_depth;
    return true;
}
bool ParserVariableArityOperatorList::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)