scripts: Add shfmt

[aarnq]

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What kind of PR is this?

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• kind/feature
• kind/improvement
• kind/deprecation
• kind/documentation
• kind/clean-up
• kind/bug
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Breaking changes should be marked kind/admin-change or kind/dev-change depending on type
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What does this PR do / why do we need this PR?

Enforces certain styling to bash scripts, especially indentation.
Let me know if there is something that seems off.

Information to reviewers

I'm also looking at other tools to complement it.

Checklist

• Proper commit message prefix on all commits
• Change checks:
  • The change is transparent
  • The change is disruptive
  • The change requires no migration steps
  • The change requires migration steps
  • The change upgrades CRDs
  • The change updates the config and the schema
• Documentation checks:
  • The public documentation required no updates
  • The public documentation required an update - [link to change](set-me)
• Metrics checks:
  • The metrics are still exposed and present in Grafana after the change
  • The metrics names didn't change (Grafana dashboards and Prometheus alerts are not affected)
  • The metrics names did change (Grafana dashboards and Prometheus alerts were fixed)
• Logs checks:
  • The logs do not show any errors after the change
• Pod Security Policy checks:
  • Any changed pod is covered by Pod Security Admission
  • Any changed pod is covered by Gatekeeper Pod Security Policies
  • The change does not cause any pods to be blocked by Pod Security Admission or Policies
• Network Policy checks:
  • Any changed pod is covered by Network Policies
  • The change does not cause any dropped packets in the NetworkPolicy Dashboard
• Audit checks:
  • The change does not cause any unnecessary Kubernetes audit events
  • The change requires changes to Kubernetes audit policy
• Falco checks:
  • The change does not cause any alerts to be generated by Falco
• Bug checks:
  • The bug fix is covered by regression tests

[simonklb]

Love seeing us making use of more linters! 👍