Automatic merge from submit-queue. 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>.

Remove /ui/ redirect

The existing kube-apiserver hard-codes `/ui` to redirect to an optional add-on, which is not appropriate. It does not work in the following scenarios:
* https-enabled dashboards
* the dashboard is deployed to a different namespace or service name
* the dashboard is not installed at all
* authorization is enabled and does not allow access to /ui

This PR removes the hard-coded `/ui` redirect.

```release-note
apiserver: the /ui kube-dashboard redirect has been removed. Follow instructions specific to your deployment to access kube-dashboard
```