Secret Detection False Positive Detection – Backend – Create audit event
# TL;DR
Add audit event logging when the `duo_secret_detection_fp_enabled` setting is changed.
## Feature Flag
Uses existing feature flag: `update_false_positive_setting_permission` (from [&22422](https://gitlab.com/groups/gitlab-org/-/work_items/22422))
## Acceptance Criteria
- [ ] Audit event is recorded when `duo_secret_detection_fp_enabled` is enabled
- [ ] Audit event is recorded when `duo_secret_detection_fp_enabled` is disabled
- [ ] Audit event includes relevant details (user, project, old value, new value)
## Implementation Details
Follow the same audit event pattern established for SAST VR and SAST FP Detection.
**Reference:** See #603463 for the SAST FP Detection audit event implementation.
issue