ENH: Add timetz attribute to DatetimeIndex and Timestamp
Currently `DatetimeIndex.time` returns a numpy array of local `datetime.time`s. In #18461, the resulting `datetime.time`s gained timezone information (but was an undocumented changed) and was subsequently reverted in #21281. Having `.time` return timezone information would still be a nice enhancement.

If we allow `DatetimeIndex.time` to return timezone information, [`timeseries.rst`](http://pandas.pydata.org/pandas-docs/stable/timeseries.html?highlight=weekofmonth#time-date-components) will need to be changed since it currently indicates that `.time` does not return timezone information.
