[FEA] Series dayofyear / day_of_year

[beckernick]

While exploring our current datetime functionality in libcudf, I noticed that we have a libcudf implementation for day_of_year that isn't accessible in cuDF Python (and last_day_of_month, which I'll file separately for dt.is_month_end). We should plumb this up to Python and make it accessible through the Series.dt accessor.

cudf/cpp/include/cudf/datetime.hpp

Lines 156 to 158 in e6a0fe3

	std::unique_ptr<cudf::column> day_of_year(
	cudf::column_view const& column,
	rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());

import pandas as pd
s = pd.Series(["2021-01-08", "2021-06-28", "2020-03-09", "2021-06-30"], dtype="datetime64[ms]")
print(s.dt.dayofyear)
print(s.dt.day_of_year)
0      8
1    179
2     69
3    181
dtype: int64
0      8
1    179
2     69
3    181
dtype: int64