Add linter to warn for python implicit concatenation

[jeffreykennethli]

As seen in this blog post, it's easy to make mistakes when using python implicit string concatenation (5% of repos, including popular ones like tensorflow, v8, pytorch make mistakes related to this). For example:

example_list = [
    "a",
    "b"
    "c"
]
# results in ["a", "bc"]

To avoid this we can try Code Review Doctor (paid) or try this flake8 rule: https://pypi.org/project/flake8-no-implicit-concat/.