Add shell-check ignore for issues we are confident in handling

[olivergondza]

Using strict mode prevents certain shellcheck issues to happen. They can be ignored per entire file[1], so they are a good candidate to make part of the preamble.

Example issue: https://github.com/koalaman/shellcheck/wiki/SC1094

https://github.com/koalaman/shellcheck/wiki/Ignore#ignoring-all-instances-in-a-file-044