Remove Kenna Security Integration in June 2028

### Current Behavior

Kenna Security integration

### Proposed Behavior

CISCO has announced that Kenna Security is EOL. The last date of entitlement is June 30, 2028. This ticket is to track the eventual removal of Kenna from Dependency-Track on or slightly before June 2028.

https://www.cisco.com/c/en/us/products/collateral/security/vulnerability-management/vm-vi-appsec-eol.html

### Checklist

- [x] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/hyades/blob/main/CONTRIBUTING.md#filing-issues)
- [x] I have checked the [existing issues](https://github.com/DependencyTrack/hyades/issues) for whether this enhancement was already requested