Conform the code to the lint rule.

[llamerada-jp]

What

This issue is a follow-up to #760.

We applied kubebuilder go/v4 template in #760, go/v4 template uses golangci-lint for linter and contains default lint rules. However, the rule is commented out because there are many violations in the existing code. Therefore, we want to update the code to conform to the rules.

How

Enable the lint rule and modify the code according to its warnings.

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions

[github-actions]

This issue has been automatically marked as stale because it has not had any activity for 30 days. It will be closed in a week if no further activity occurs. Thank you for your contributions.