ENH: pandas.Timestamp.round infer correct timezone around DST
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [x] (optional) I have confirmed this bug exists on the master branch of pandas.

---

**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
import pandas as pd
from datetime import timedelta as td

test_ts = pd.Timestamp('2020-11-02 05:00:01.167', tz='UTC')
lt_ts = test_ts.tz_convert('America/New_York')
lt_ts
# Timestamp('2020-11-02 00:00:01.167000-0500', tz='America/New_York')
lt_ts -= td(days=1)
lt_ts
# Timestamp('2020-11-01 01:00:01.167000-0400', tz='America/New_York')
lt_ts.round(freq='H')



Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "pandas/_libs/tslibs/timestamps.pyx", line 1145, in pandas._libs.tslibs.timestamps.Timestamp.round
  File "pandas/_libs/tslibs/timestamps.pyx", line 1099, in pandas._libs.tslibs.timestamps.Timestamp._round
  File "pandas/_libs/tslibs/timestamps.pyx", line 1317, in pandas._libs.tslibs.timestamps.Timestamp.tz_localize
  File "pandas/_libs/tslibs/tzconversion.pyx", line 63, in pandas._libs.tslibs.tzconversion.tz_localize_to_utc_single
  File "pandas/_libs/tslibs/tzconversion.pyx", line 275, in pandas._libs.tslibs.tzconversion.tz_localize_to_utc
pytz.exceptions.AmbiguousTimeError: Cannot infer dst time from 2020-11-01 01:00:00, try using the 'ambiguous' argument

```

#### Problem description

pandas.Timestamp.round method crashes.

#### Expected Output
```python
Timestamp('2020-11-01 01:00:00.0000-0400', tz='America/New_York')
```
#### Output of ``pd.show_versions()``

<details>

pd.show_versions()
INSTALLED VERSIONS
------------------
commit           : 67a3d4241ab84419856b84fc3ebc9abcbe66c6b3
python           : 3.8.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.0-52-generic
Version          : #57-Ubuntu SMP Thu Oct 15 10:57:00 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_GB.UTF-8
LOCALE           : en_GB.UTF-8
pandas           : 1.1.4
numpy            : 1.19.2
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.3
setuptools       : 50.3.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.8.3 (dt dec pq3 ext lo64)
jinja2           : 2.11.2
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.1
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.2
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
