Rename starboard to container_scanning for operational vulnerabilities

What does this MR do and why?

This MR renames starboard configuration block in GitLab Agent for Kubernetes configuration file to container_scanning with note that starboard keyword is deprecated and will be removed in 16.0.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #368828 (closed)