Support is_dst indicators in tz_localize

The indicators are useful for assigning the correct offset when there are ambiguous transition times closes #7943.
Three things:
    * I think the option to raise should be `raise`, rather than `None`
    * I think the default should be `True` (which broadcasts to the `bool-ndarray` case) instead of `raise`-- raising on a vectorized operation seems bad when the rest of the array is valid.
    * I feel like the `bool-ndarray` doc could be more clear.  Something like this: "-bool-ndarray is an array of flags indicating whether to take the first (True) or last (False) of the possible localizations.  If the ambiguity is a 'fall back' DST transition, this flag will be True for DST and False for standard time."