Get the shellcheck CI job to pass again by addressing the issues it
flagged across our shell scripts.
Note: I am not 100% sure of every fix applied here. Reviewers should
feel free to challenge specific changes and suggest better ones
where relevant.
Improved script portability by switching to `/usr/bin/env bash`, ensuring
better support across environments where `bash` may not be the default shell.
Few scripts were duplicated between the scripts and the bin folders.
Reorganize the scripts in a common folder, and align filenames to
follow the same rule.
lebaudantoine