Automatic merge from submit-queue (batch tested with PRs 67894, 64097). 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>.
HPA metrics specificity improvements
**What this PR does / why we need it**:
Improves available specificity for HPA metrics by adding metric selector fields for metrics of Pods and Objects.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Implements this KEP: https://github.com/kubernetes/community/pull/2055
**Special notes for your reviewer**:
Need to add/update tests?
**Release note**:
```release-note
Introduces autoscaling/v2beta2 and custom_metrics/v1beta2, which implement metric selectors for Object and Pods metrics, as well as allowing AverageValue targets on Objects, similar to External metrics.
```
/assign @DirectXMan12
Kubernetes-commit: fdb5707194d56cbbd0da11c5be3a2a5653e714c9
