[DOC] Rolling window apply with constant parameters.

## Report incorrect documentation

**Location of incorrect documentation**
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.window.rolling.Rolling.apply.html?highlight=apply#pandas.core.[…]olling.apply

**Describe the problems or issues found in the documentation**
Is the rolling apply fully implemented? `args` and `kwargs` seem to be ignored, or I am doing it wrong. I searched far and wide for examples of how to add a constant parameter for this function (like decay rate) but I have not found it.

Looking at the implementation in Github https://github.com/rapidsai/cudf/blob/c929ba1fe85c152d6e8b4c868cd36f0802dafa51/python/cudf/cudf/core/window/rolling.py#L254 it also does not become directly clear how to use it. `args` and `kwargs` are not referenced.

**Steps taken to verify documentation is incorrect**
List any steps you have taken:
Looked at the source code and examples.

**Suggested fix for documentation**
Detail proposed changes to fix the documentation if you have any.
Give an example usage of the rolling apply with a constant parameter (for example, decay rate).
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## Report needed documentation

**Report needed documentation**
A lot of rolling functions will have some kind of configuration parameters that are required. It should be possible to pass them.

**Describe the documentation you'd like**
Either documentation giving examples for this use case should be added, or if the feature is forgotten, the feature should be completed.

**Steps taken to search for needed documentation**
List any steps you have taken:
- Google
- https://pandas.pydata.org/pandas-docs/stable/user_guide/window.html#rolling-window
- https://docs.rapids.ai/api/cudf/stable/api.html?highlight=apply#cudf.core.window.Rolling.apply