Feature request: improve behavior of ambiguous='infer' of tz_localize()
[I first thought it was a bug, but it is actually a missing feautre.](https://github.com/pandas-dev/pandas/issues/29031)

When I apply `tz_localize()` I run in the following error:

    AmbiguousTimeError: There are %i dst switches when there should only be 1.

Here is my code to reproduce the error. Note that from 2am to 3am every datetime is a duplicate due to daylight saving time.

    index = pd.DatetimeIndex(['2018-10-28 01:00:00', '2018-10-28 01:15:00',
                              '2018-10-28 01:30:00', '2018-10-28 01:45:00',
                              '2018-10-28 02:00:00', '2018-10-28 02:00:00',
                              '2018-10-28 02:15:00', '2018-10-28 02:15:00',
                              '2018-10-28 02:30:00', '2018-10-28 02:30:00',
                              '2018-10-28 02:45:00', '2018-10-28 02:45:00',
                              '2018-10-28 03:00:00', '2018-10-28 03:15:00',
                              '2018-10-28 03:30:00', '2018-10-28 03:45:00',
                              '2018-10-28 04:00:00'], freq='infer')
    
    data = list(range(len(index)))
    
    df = pd.DataFrame(data=data,index=index)
    df.index = df.index.tz_localize('Europe/Berlin', ambiguous='infer')

I propose to improve the behavior of `infer`. The problem here is daylight saving time. 
I propose: With respect to the order, duplicates are identified as winter or summer time.

The result should be an index looking like this:
```
2018-10-28 01:00:00+02:00
2018-10-28 01:15:00+02:00
2018-10-28 01:30:00+02:00
2018-10-28 01:45:00+02:00
2018-10-28 02:00:00+02:00
2018-10-28 02:00:00+01:00
2018-10-28 02:15:00+02:00
2018-10-28 02:15:00+01:00
2018-10-28 02:30:00+02:00
2018-10-28 02:30:00+01:00
2018-10-28 02:45:00+02:00
2018-10-28 02:45:00+01:00
2018-10-28 03:00:00+01:00
2018-10-28 03:15:00+01:00
2018-10-28 03:30:00+01:00
2018-10-28 03:45:00+01:00
2018-10-28 04:00:00+01:00
```
I think this is "easily" possible and it's logical: 
For example 2am occurs two times, than the "earlier 2am" must be `2018-10-28 02:00:00+02:00` and the "later 2am" must be `2018-10-28 02:00:00+01:00`

I can help with further explanations.
This is my first feature request.
I have never done a pull request, but I might do one -- let me know if that makes sense. I am not the most experienced python developer but I don't know how to find out wheather I can contribute. 