Add audit event for Secret Detection False Positive Detection setting

What does this MR do?

Adds a new audit event type duo_secret_detection_fp_detection_enabled_updated that is triggered when the G_itLab Duo Secret Detection False Positive Detection_ feature enabled setting is changed on a project by a Security Manager.

This follows the same pattern established by the SAST FP Detection audit event (duo_sast_fp_detection_enabled_updated). The logic lives under the same feature flag (update_false_positive_detection_setting_permission) as we use for duo_sast_fp_detection_enabled_updated.

References

• Project epic: SAST False Positive Detection - Add permission ... (gitlab-org#22422 - closed) • Charlie Kroon • 19.2
  • Epic Phase Epic: Secret Detection False Positive Detection - Add... (gitlab-org#22425 - closed) • Charlie Kroon • 19.2
  • Closes Secret Detection False Positive Detection – Bac... (#603477 - closed) • Charlie Kroon • 19.2
• Reference implementation: SAST False Positive Detection - Backend - Creat... (!241556 - merged) • Charlie Kroon • 19.2