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.