Doc improvements

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

I'm trying to use documentation to understand the arguments to functions in [`functions.py`](https://github.com/apache/datafusion-python/blob/ad8d41f2b5faff9a35aeeb340a24480c8ccb6eff/python/datafusion/functions.py).

**Describe the solution you'd like**

I'd love if all the function docstrings had documentation for the arguments to the function. For example, [`alias` has descriptions of its arguments](https://github.com/apache/datafusion-python/blob/ad8d41f2b5faff9a35aeeb340a24480c8ccb6eff/python/datafusion/functions.py#L494-L497).

**Describe alternatives you've considered**

None, really, just recording it as a unit of work that would improve the project.

**Additional context**

This is a follow-on issue to @ntjohnson1 excellent work in https://github.com/apache/datafusion-python/pull/1435 where he added tons of helpful examples. I was browsing the code in the PR and realized quite a few functions were missing argument documentation.

首先閱讀 python/datafusion/functions.py，並將 alias docstring 與其他 function docstrings 進行比較。找出引數缺少描述的函式，並參照現有範例，以一致的方式為它們撰寫文件。當該檔案中的所有 function docstrings 都包含引數文件時，工作即告完成。

由索引模型根據 Issue 內容生成。