Add the option to enable default Pod Security Configuration (#9017)

* Add the option to enable default Pod Security Configuration

Enable Pod Security in all namespaces by default with the option to
exempt some namespaces. Without the change only namespaces explicitly
configured will receive the admission plugin treatment.

* Fix the PR according to code review comments

* Revert the latest changes

- leave the empty file when kube_pod_security_use_default, but add comment explaining the empty file
- don't attempt magic at conditionally adding PodSecurity to kube_apiserver_admission_plugins_needs_configuration