Automatic merge from submit-queue (batch tested with PRs 39648, 38167, 39591, 39415, 39612)
Add hack/verify-readonly-packages.sh
Create a `.readonly` file in a package. Any change between `$KUBE_VERIFY_GIT_BRANCH` and `HEAD` will lead to output like:
```shell
$ hack/verify-readonly-packages.sh
Readonly packages changed compared to "master" branch: pkg/generated
```
This is part of https://github.com/kubernetes/kubernetes/issues/39528