Automatic merge from submit-queue (batch tested with PRs 58540, 62314). 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>.
Add ability to specify port for kubeadm `API.ControlPlaneEndpoint`
**What this PR does / why we need it**:
When `API.ControlPlaneEndpoint` is used, the `BindPort` of the
apiserver is currently assumed, which means a load balancer cannot
listen on a different port than the apiserver. This extends the
`ControlPlaneEndpoint` to take an optional port which may differ
from the apiserver's `BindPort`.
**Release note**:
```release-note
The kubeadm config option `API.ControlPlaneEndpoint` has been extended to take an optional port which may differ from the apiserver's bind port.
```
When `API.ControlPlaneEndpoint` is used, the `BindPort` of the
apiserver is currently assumed, which means a load balancer cannot
listen on a different port than the apiserver. This extends the
`ControlPlaneEndpoint` to take an optional port which may differ
from the apiserver's `BindPort`.
Previously, kubeadm would use <ip>:<port> to construct a master
endpoint. This works fine for IPv4 addresses, but not for IPv6.
IPv6 requires the ip to be encased in brackets when being joined
to a port with a colon.
This patch updates kubeadm to support wrapping a v6 address with
[] to form the master endpoint url. Since this functionality is
needed in multiple areas, a dedicated util function was created.
Fixes: https://github.com/kubernetes/kubernetes/issues/48227
