Add pre-commit hook `shellcheck-py` to standardize shell files

[jbampton]

https://github.com/shellcheck-py/shellcheck-py

https://www.shellcheck.net/

https://github.com/koalaman/shellcheck

Example .pre-commit-config.yaml entry:

 - repo: https://github.com/shellcheck-py/shellcheck-py
   rev: v0.10.0.1
   hooks:
     - id: shellcheck

Example .shellcheckrc config file:

disable=SC2004,SC2041,SC2155,SC2181

There are various ways you can ignore errors:

https://github.com/koalaman/shellcheck/wiki/Ignore

[dave2wave]

Go ahead!

[sbp]

Resolved by abdd110. I copied our configuration from ATR.