ci(lint): add shell linter - Differential ShellCheck

[jamacku]

Differential ShellCheck is a GitHub action that performs differential ShellCheck scans on shell scripts changed via PR and reports results directly in PR. The beauty of differential scans is that you will get reports only about newly added defects.

Since this repository has few shell scripts, I think you might find some value in having a shell linter. Differential ShellCheck action is able to produce reports in SARIF format. GitHub understands this format and is able to display it nicely as a PR comment, and on the Files Changed tab, please see below.

Documentation is available at @redhat-plumbers-in-action/differential-shellcheck. Let me know If you are missing some feature or setting. I'm always happy to extend functionality.

[praiskup]

+1