BUG: to_sql not properly escaping column names postgresql
- [x] I have checked that this issue has not already been reported.
Although, this issue seems relevant: https://github.com/pandas-dev/pandas/issues/6796
- [x] I have confirmed this bug exists on the latest version of pandas.

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

---

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

```python
# Your code here
>>> from sqlalchemy import create_engine
>>> eng = create_engine(postgesql-dsn)

>>> pd.DataFrame({'(abc]': [1,2,3]}).to_sql('tbl', eng, if_exists='replace')
KeyError: '(abc])s'

>>> pd.DataFrame({'(abc)': [1,2,3]}).to_sql('tbl', eng, if_exists='replace')
KeyError: '(abc'

>>> pd.DataFrame({'[abc)': [1,2,3]}).to_sql('tbl', eng, if_exists='replace')
KeyError: '[abc'
```

#### Problem description

I noticed that `to_sql` throws an error when column names have a combination of `(` and `]`s in them. I didn't try this across all sql flavors, but I didn't run into issues with sqlite so I'm guessing this is tied to psycopg2 variable identifier substitution.

#### Expected Output

No KeyErrors

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : f2c8480af2f25efdbd803218b9d87980f416563e
python           : 3.8.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.19.128-microsoft-standard
Version          : #1 SMP Tue Jun 23 12:58:10 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : C.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.2.3
numpy            : 1.19.4
pytz             : 2020.4
dateutil         : 2.8.1
pip              : 20.0.2
setuptools       : 45.2.0
Cython           : 0.29.21
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.8.6 (dt dec pq3 ext lo64)
jinja2           : 2.10.1
IPython          : 7.19.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : 1.2.0
xlwt             : None
numba            : None


</details>
