Hope select function, "top_k" and "bottom_k", could support "group by level"

### Discussed in https://github.com/apache/iotdb/discussions/3888

I find we can use `group by level` to get the effect of merging devices when using aggregation function. Hope select function, `top_k` and `bottom_k`, could support `group by level` as well.

从 https://github.com/apache/iotdb/discussions/3888 中链接的讨论开始，并将聚合函数现有的 `group by level` 行为与 `top_k` 和 `bottom_k` 进行比较。当两个 select 函数支持按层级分组，且行为与聚合查询一致（包括 issue 中所示的情况）时，即视为完成。

由索引模型根据 Issue 内容生成。