Run shellcheck in pre-commit

[martinhoyer]

Wouldn't it make sense to add shellcheck-precommit hook to pre-commit config instead of having a dedicated github action and all that goes with it?

From what I understand, the point of differential-shellcheck is that it checks only changed files, which is what pre-commit is doing.

We could also remove the .shellcheckrc file, which only includes external-sources=true and add it as an argument in pre-commit-config.yaml. (assuming people are not running shellcheck manually and instead rely on pre-commit locally)