Automatic merge from submit-queue (batch tested with PRs 61400, 61048). 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>.
code-gen: allow specifying custom resync periods for certain informer types
**What this PR does / why we need it**:
This PR extends the informer code-generator to allow the consumer to specify a custom resync period for certain informer types and uses the default resync period if none is defined.
**Special notes for your reviewer**:
Example:
```go
cs := clientset.NewForConfigOrDie(config)
resyncConfig := externalversions.ResyncConfiguration{
&samplev1alpha1.Sample{}: 30 * time.Second,
}
informer := externalversions.NewSharedInformerFactory(cs, 2*time.Minute, externalversions.WithCustomResyncConfig(resyncConfig))
```
**Release note**:
```release-note
NONE
```
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