Adding shellcheck static analysis in CI

[Buzz-Lightyear]

This PR adds shellcheck static analysis for the shell scripts in this repo and addresses the warnings currently present:

In ./script/kind/usr/local/bin/kind-entrypoint.sh line 33:
exec $@
     ^-- SC2068 (error): Double quote array expansions to avoid re-splitting elements.


In ./script/rootless/common.sh line 1:
export REPO_DIR=$(git rev-parse --show-toplevel)
^-- SC2148 (error): Tips depend on target shell and yours is unknown. Add a shebang or a 'shell' directive.
       ^------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
...
...

[elpdt852]

Thanks @Buzz-Lightyear ! This looks good to me.