Improvement: Introduce webhook mechanism to trigger the workloads assessments

[4everming]

Describe the solution you'd like For now, scanning in this project is triggered by cronjobs periodically. In this case, the changes such as workload creation/termination/update during the scanning interval will not be aware. That would potentially cause some problems. A hook mechanism should be introduced so that we can know everything that happened to the cluster once the policy has been created, no matter what scanning interval is configured.