Automatic merge from submit-queue (batch tested with PRs 61378, 60915, 61499, 61507, 61478). 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>.
Capture pod startup phases as metrics
Learning from https://github.com/kubernetes/kubernetes/issues/60589, we should also start collecting and graphing sub-parts of pod-startup latency.
/sig scalability
/kind feature
/priority important-soon
/cc @wojtek-t
```release-note
NONE
```
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