Add ShellCheck linter target

[supersven]

It lints all shell scripts that are not excluded, i.e. new ones and old ones without issues. Excluded are those that currently have issues. They should be fixed on a step-by-step basis. This conservative/careful approach is necessary due to shell scripts having neither a type checker nor tests. "Surprises" should be avoided, especially as they might
appear in stressful situations.

This PR supersedes #2310 . In that PR I learned that even simple looking quotes may lead to awful errors.

https://wearezeta.atlassian.net/browse/SQPIT-279

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• If this PR changes development workflow or dependencies, they have been A) automated and B) documented under docs/developer/. All efforts have been taken to minimize development setup breakage or slowdown for co-workers.
  schema`** to update the cassandra schema documentation.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.

[akshaymankar]

We should create issues to fix the ignored scripts if we really want to do the FUTUREWORK.
Approving since this is still an improvement.

[supersven]

@akshaymankar , Good idea 👍

I've created tasks/tickets for the ignored files: https://wearezeta.atlassian.net/browse/SQPIT-952