Add shell CI/CD linter and fix lint issues

[epiccurious]

Is your feature request related to a problem? Please describe.
Add automated linters for shell and python to the repo.

Describe the solution you'd like
Every time there's commit to master or any PR, run shell and Python linters.

Describe alternatives you've considered
The user and reviewer could run linters manually, but it's hard to enforce that behavior.

Additional context
We'll need to identify which linter checks to exclude, based on @BenWestgate's preference. For example, shellcheck enforces ${variable_name} instead of $variable_name which is nice but optional in many cases.

[BenWestgate]

Seems like a good solution that'll make higher quality PRs.

@epiccurious I don't care if it puts {} around variable names or not, you can decide. Check the code formatting both ways and see what is easier to read, if drawn use the shellcheck defaults. I obviously typed it without curly braces to save time because I know where they are not needed.

[epiccurious]

Ok. I'll exclude the nit rule for double-quoting variables. For reference, here's the documentation for it https://www.shellcheck.net/wiki/SC2086

[BenWestgate]

Ok. I'll exclude the nit rule for double-quoting variables. For reference, here's the documentation for it https://www.shellcheck.net/wiki/SC2086

I don't mind if it puts double quotes around variables either. Less custom rules is better, but less work complying with the rules is best.

When I worked on Tails, my IDE reformatted a lot of the python automatically and it was a pain to work on. Almost that same week after they saw my struggle they added a python code formater to their linter/ci/cd/xkwjuhaishdflp! thing.

[epiccurious]

Ok I'll remove this rule exception and reformat with double-quotes.

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