Notification enabled by default even when there is no valid configuration

Created by: zryfish

Describe the bug Platform notifications are all enabled by default even there are no valid configurations.

Versions used(KubeSphere/Kubernetes) KubeSphere: nightly-20210321 Kubernetes: (If KubeSphere installer used, you can skip this)

/assign @kubesphere/sig-console /milestone 3.1.0 /kind bug