add exists_ok param to add_column

[talevy42]

No description provided.

[shaunagm]

In addition to the parameter rename, you'll also need to lint the contribution. The new docs that show you how to do it are finally live! Sorry that they were missing before. You can see the instructions here: https://move-coop.github.io/parsons/html/stable/contributing.html#linting

Running Black locally and committing the changes should fix any issues.

[shaunagm]

Can you see the test results? If not, here they are:

=================================== FAILURES ===================================
__________________ TestParsonsTable.test_add_column_exists_ok __________________

self = <test.test_etl.TestParsonsTable testMethod=test_add_column_exists_ok>

    def test_add_column_exists_ok(self):
>       self.tbl.add_column("first", exists_ok=True)
E       TypeError: ETL.add_column() got an unexpected keyword argument 'exists_ok'

test/test_etl.py:309: TypeError
=============================== warnings summary ===============================
venv/lib/python3.10/site-packages/joblib/my_exceptions.py:21
  /home/circleci/repo/venv/lib/python3.10/site-packages/joblib/my_exceptions.py:21: DeprecationWarning: TransportableException is deprecated and will be removed from joblib in 0.16
    warn("{} is deprecated and will be removed from joblib "

test/test_etl.py::TestParsonsTable::test_from_petl
test/test_etl.py::TestParsonsTable::test_from_petl
test/test_etl.py::TestParsonsTable::test_from_petl
  /home/circleci/repo/venv/lib/python3.10/site-packages/petl/util/random.py:170: DeprecationWarning: Seeding based on hashing is deprecated
  since Python 3.9 and will be removed in a subsequent version. The only 
  supported seed types are: None, int, float, str, bytes, and bytearray.
    random.seed(seed)

test/test_gmail/test_gmail.py: 10 warnings
  /home/circleci/repo/venv/lib/python3.10/site-packages/httplib2/__init__.py:147: DeprecationWarning: ssl.PROTOCOL_TLS is deprecated
    context = ssl.SSLContext(DEFAULT_TLS_VERSION)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================== short test summary info ============================
FAILED test/test_etl.py::TestParsonsTable::test_add_column_exists_ok - TypeEr...
===== 1 failed, 667 passed, 182 skipped, 1 xfailed, 14 warnings in 22.65s ======

Exited with code exit status 1

CircleCI received exit code 1
`

[shaunagm]

Thanks for making the variable name changes! This looks ready to merge.