Automatic merge from submit-queue (batch tested with PRs 57672, 60299, 59757, 60283, 60265). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Add a metric exposing number of objects per type
Fix#51953
Adds a goroutine that periodically checks the count of objects in etcd and publishes a metric with this data.
```release-note
APIserver backed by etcdv3 exports metric showing number of resources per kind
```
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