DOC: DateOffset docs missing details on `weekday` argument and has incorrect link for `relativedelta`

[Dr-Irv]

Pandas version checks

• I have checked that the issue still exists on the latest versions of the docs on main here

Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.tseries.offsets.DateOffset.html

Documentation problem

First, the weekday argument has a type that comes from relativedelta that is class weekday

Second, the link to dateutil.relativedelta.relativedelta is going to matplotlib, but it really should go to dateutil: https://dateutil.readthedocs.io/en/stable/relativedelta.html

Suggested fix for documentation

1. Fix the link to go to the relativedelta docs, not matplotlib
2. Document that weekday has a special type for its argument.

[TeoSkondras]

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[Detoro]

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