Report vulnerability on unsupported OS

• Please check this box if this contribution uses AI-generated content (including content generated by GitLab Duo features) as outlined in the GitLab DCO & CLA

What does this MR do?

This merge request allow the addition of a finding when the OS is detected to be no longer supported.

By default the feature is not enabled and can be controlled with the following variables:

Variable	Default Value	Description
CS_REPORT_OS_EOL	""	When this variable is set and the OS is detected to be no longer supported a vulnerability will be added to the report with the severity defined by the value of the CS_REPORT_EOL_SEVERITY variable.
CS_REPORT_EOL_SEVERITY	Critical	The severity associated with a no longer supported OS. This could be any of the possible severity. If the severity is invalid or not defined the default Critical severity will be used.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer