Configuration file improvements

[craddm]

Some of the config values are confusing and/or vestigial, needing better explanation, to be shifted to optional, or removing once and for all.

1. having a separate "harbor_ip" field is confusing and unnecessary, it is not used on Dawn and is unnecessary on AKS as the IP address can now be allocated automatically and passed through the stack1.
2. add better explanation of the isolated cluster api endpoint field1.
3. fridge_api_ip_address can be a dummy value on Dawn at present