Adopt Isolated Cluster creation to the new possibility of machine / firewall creation with DNS and NTP Servers

[majst01]

Since metal-stack/metal-api#571 it is possible to specify DNS and NTP Servers during machine/firewall creation. This enables us to simplify the logic to modify the DNS and NTP Server configuration with the help of the os-metal-extension.

Instead we should adopt the machine/firewall creation process to put the DNS and NTP Servers given in the cloud profile for isolated clusters to the allocation.

This needs to be adopted in:

• this repo
• the os-metal-extension
• machine-controller-manager-metal

If in a specific partition these parameters are defined, the parameters from the cloud profile must be of higher precedence.

@Gerrit91 @mwennrich @simcod @vknabel @robertvolkmann Please add comments if required.

[robertvolkmann]

Please mind the documentation: https://github.com/metal-stack/docs/blob/master/docs/src/overview/isolated-kubernetes.md