Add human-readable override action display to policy drawer

What does this MR do and why?

Add human-readable override action display to policy drawer

Update vulnerability management policy drawer to display override actions in a human-readable format. This supports the severity override feature that allows users to automatically adjust vulnerability severity based on criteria like CVE/CWE identifiers.

• Add humanizeOverrideAction() and isOverrideAction() utils
• Update details_drawer.vue to render override action details
• Display action text like 'Set to High' or 'Increase by one level'
• Add tests for new functionality

Changelog: added EE: true

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Related to #589442 (closed)