See #7233
The controlplane label is simply injected into existing controller-based
node label flow.
For controlplane taint default NoScheduleTaint, additional controller &
resource was implemented to handle node taints.
This also fixes a problem with `allowSchedulingOnControlPlanes` not
being reactive to config changes - now it is.
Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>