Rename weekday and weekday0 kernels to to num_days_from_monday and days_since_sunday

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Depending on the usecase sometimes one wants the days of week to start from Sunday or Monday. Dates 🤷

@ovr added the weekday0 kernel in #2052

But now the names are weekday and weekday0 which I think might be confusing to the average reader

Describe the solution you'd like
I propose we follow the chrono naming scheme num_days_from_sunday and num_days_from_monday

https://docs.rs/chrono/0.4.19/chrono/enum.Weekday.html#method.num_days_from_sunday
https://docs.rs/chrono/0.4.19/chrono/enum.Weekday.html#method.num_days_from_monday

Describe alternatives you've considered
We could do nothing and handle any potential confusion with documentation

Additional context
Add any other context or screenshots about the feature request here.