kubeadm-setup: add page about control plane flags

This page adds instructions on how to use the kubeadm config
to pass flags to control plane components.

The provided examples are pretty basic. Later this can be expanded with
actual user stories.

content/en/docs/setup/independent/control-plane-flags.md

@@ -0,0 +1,59 @@
+---
+reviewers:
+- fabriziopandini
+- luxas
+- timothysc 
+title: Customizing control plane flags with kubeadm
+---
+
+{{% capture overview %}}
+
+kubeadm’s configuration exposes the following fields that can be used to override the default flags passed to control plane components such as the APISever, ControllerManager and Scheduler:
+
+- `APIServerExtraArgs`
+- `ControllerManagerExtraArgs`
+- `SchedulerExtraArgs`
+
+The fields can contain a list of `key: value` pairs. To override flags for a specific control plane component just include one of the fields above and start adding flags for it.
+
+{{< note >}}
+In later versions of the kubeadm configuration these fields will be replaced by usage of a ComponentConfig and a ConfigMap.
+{{< /note >}}
+
+{{% /capture %}}
+
+## APIServer flags
+
+The list of possible APIServer flags and their descriptions can be found [here](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/).
+
+Example usage:
+```yaml
+apiServerExtraArgs:
+  advertise-address: 192.168.0.103
+  allow-privileged: true
+  anonymous-auth: false
+```
+
+## ControllerManager flags
+
+The list of possible ControllerManager flags and their descriptions can be found [here](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-controller-manager/).
+
+Example usage:
+```yaml
+controllerManagerExtraArgs:
+  cluster-signing-key-file: /home/johndoe/keys/ca.key
+  bind-address: 192.168.0.101
+  deployment-controller-sync-period: 50
+```
+
+## Scheduler flags
+
+The list of possible Scheduler flags and their descriptions can be found [here](https://kubernetes.io/docs/reference/command-line-tools-reference/kube-scheduler/).
+
+Example usage:
+```yaml
+schedulerExtraArgs:
+  address: 192.168.0.104
+  config: /home/johndoe/schedconfig
+  master: 192.168.0.103
+```