Automatic merge from submit-queue (batch tested with PRs 65730, 66615, 66684, 66519, 66510). 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>.

Speed up HPA reaction to metric changes by removing scale up forbidden window

**What this PR does / why we need it**:
Speed up HPA reaction to metric changes by removing scale up forbidden window.

Scale up forbidden window was protecting HPA against making decision to scale up based on metrics gathered during pod initialisation (which may be invalid, for example pod may be using a lot of CPU despite not doing any "actual" work).

To avoid that negative effect only use per pod metrics from pods that are:
- ready (so metrics about them should be valid), or
- unready but creation and last readiness change timestamps are apart more than 10s (pods that have formerly been ready and so metrics are in at least some cases (pod becoming unready because of overload) very useful).


This PR only deals with scale up window. I'll send another PR dealing with scale down window soon.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:

**Special notes for your reviewer**:

**Release note**:
```release-note
Speed up HPA reaction to metric changes by removing scale up forbidden window.

Scale up forbidden window was protecting HPA against making decision to scale up based on metrics gathered during pod initialisation (which may be invalid, for example pod may be using a lot of CPU despite not doing any "actual" work).

To avoid that negative effect only use per pod metrics from pods that are:
- ready (so metrics about them should be valid), or
- unready but creation and last readiness change timestamps are apart more than 10s (pods that have formerly been ready and so metrics are in at least some cases (pod becoming unready because of overload) very useful).
```