Add https://github.com/koalaman/shellcheck-precommit

We should add a linter for sh files.

https://github.com/koalaman/shellcheck-precommit

In both base-worker and the worker template.

changed milestone to %0.3.7

added P3 Quick Win labels

assigned to @ebardou

mentioned in merge request !518 (merged)

closed with merge request !518 (merged)