[7.0.x] Update system pods check

[bernardjkim]

Description

Update system pods check. This patch will help reduce the load on etcd if there are a large number of pods in user namespaces. System pods check will only search the kube-system and monitoring namespaces for system pods.

Linked tickets and PRs

• Requires gravitational/satellite#281
• Ports https://github.com/gravitational/planet/pull/772