[FEA] Support use_na_sentinel in factorize

[brandon-b-miller]

Is your feature request related to a problem? Please describe.

EDITED 12/16/2022
As of pandas 1.5, the na_sentinel parameter is deprecated in favor of a boolean flag use_na_sentinel. We need to update cudf to match the new behavior to retain compatibility with pandas 2.0.

The rest of this issue's text is preserved for the record, but is no longer relevant.

ORIGINAL ISSUE INTENT

When using cudf.Series.factorize with na_sentinel=None an error is encountered, whereas pandas supports this option.

  File "/cudf/python/cudf/cudf/core/series.py", line 2517, in label_encoding                                                                                                                 
    dtype = min_scalar_type(max(len(cats), na_sentinel), 8)                                                                                                                                                          
TypeError: '>' not supported between instances of 'NoneType' and 'int'

Describe the solution you'd like
As described here When None is passed, any nans in the input data should result in nan being part of the set of uniques returned by the function. In cuDF this likely reads the same except substitute true <NA>.

Describe alternatives you've considered

Additional context
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.factorize.html

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