DOC: Template Timestamp & NaT docstrings
Currently some NaT's method docstrings directly mirror Timestamp's method docstrings via copy and pasting.

e.g.

https://github.com/pandas-dev/pandas/blob/4f717551b8e49ecd978bb4f5a985d6f6a96d86e9/pandas/_libs/tslibs/timestamps.pyx#L646-L650

https://github.com/pandas-dev/pandas/blob/4f717551b8e49ecd978bb4f5a985d6f6a96d86e9/pandas/_libs/tslibs/nattype.pyx#L368-L372

We don't want to import Timestamp into `nattype.pyx` to avoid a circular import. Ideally we should template the docstrings of both `Timestamps` and `NaT` methods to avoid this copy pasting.