Only watch Pods and Nodes when Node Watcher is enabled

[xing-yang]

In the external-health-monitor-controller, we always watch all PVCs, Pods, Nodes:
https://github.com/kubernetes-csi/external-health-monitor/blob/v0.3.0/cmd/csi-external-health-monitor-controller/main.go#L210

We need to watch them to support the Node Watcher functionality which is disabled by default. This has caused scalability problems.
https://github.com/kubernetes-csi/external-health-monitor/blob/v0.3.0/cmd/csi-external-health-monitor-controller/main.go#L66

We should change the code to only watch Pods and Nodes when the Node Watcher component is enabled.

kubernetes/kubernetes#102452 (comment)

[pohly]

It also would be useful to address the scalability issue when the Node Watcher functionality is enabled.

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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

This bot triages issues and PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the issue is closed

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• Mark this issue or PR as fresh with /remove-lifecycle rotten
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/lifecycle rotten

[pohly]

/remove-lifecycle rotten

[pohly]

/lifecycle frozen

[mowangdk]

/assign