Automatic merge from submit-queue (batch tested with PRs 51583, 51283, 51374, 51690, 51716)
Unify initializer name validation
Unify the validation rules on initializer names. Fix https://github.com/kubernetes/kubernetes/issues/51843.
```release-note
Action required: validation rule on metadata.initializers.pending[x].name is tightened. The initializer name needs to contain at least three segments separated by dots. If you create objects with pending initializers, (i.e., not relying on apiserver adding pending initializers according to initializerconfiguration), you need to update the initializer name in existing objects and in configuration files to comply to the new validation rule.
```
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