[Doc] Add how to use the wcp priviledged wcp-vmop-user-domain user

[rguske]

In TKGs, you don't have permissions to e.g. power-on, power-off or even configure the SupervisorVMs or the TKC-VMs. Not even with the administrator@vsphere.local user. Even though, there's a way to use the wcp-vmop-user-domain user in order to execute those tasks.
Add the "how to" to the TKGs guide.