build: provide ShellCheck shared workflow & template

[kdmccormick]

Description

build: provide ShellCheck shared workflow & template

We add a central shared ShellCheck workflow that can
be used from any openedx repository. It takes a small set
of parameters, which could be expanded later if needed.

We also add a workflow template for invoking the ShellCheck
workflow, which repositories can copy and use.

Supporting information

Implements the ShellCheck ADR which was introduced in:

• docs: add ADR to adopt ShellCheck #60

Here's the template in-use in edx-platform:

• build: run ShellCheck in CI edx-platform#31809

Other Information

(from edx-platform)

output from a successful build

output of a build with a shellcheck violation

output of a build that failed because no scripts were checked

[kdmccormick]

Alright, I reorganized this based on the discussions above, and this seems to be working. Some notes for reviewers.

[kdmccormick]

This check only runs on Ubuntu.

I was tempted to generalize it to MacOS. It would be easy enough to use a build matrix here so that this runs on both ubuntu-latest and macos-latest. What would be a little more difficult is ensuring that we download the correct binary in action.yml.

I decided against that because I've already been at this for a few days, and I feel like I could spend another week tweaking and perfecting everything, but it's not clear to me that it'd be time well spent. If you disagree, let me know.

[kdmccormick]

Just kidding, I thought of a way to do this that wasn't too bad.

[kdmccormick]

Alright @timmc-edx @feanil, both this and the edx-platform PR are ready for review!

[kdmccormick]

Alright @timmc-edx @feanil , I changed it back from an action to a shared workflow. Fortunately, the code seems much simpler and the output is much nicer. This and the edx-platform PR are both ready for review again.

[kdmccormick]

@feanil @timmc-edx Latest changes are:

• Rather than an include-list of directories, we check the entire repo, but allow an exclude-list to be passed in. The template excludes node_modules by default. The shared workflow excludes nothing by default. (I like that any exclude pattern must be explicitly passed into the shared workflow).
• If a bad OS argument provided, we print out the valid OS argument options.
• I'd originally had a step that checked whether the list of input files is empty, and errored if it was empty. Turns out shellcheck provides that behavior already. In order to keep the implementation as simple as possible, I removed the custom step, and will let shellcheck report that error itself.

Screenshots have also been updated.

[feanil]

Two small changes that I think are worth making for clarity but otherwise this looks good to me. I don't need to review again before you merge.