Audit required and newer configuration options added to the schema, along with versioning of the schema itself

[hedss]

No description provided.

[hedss]

For example sshKeys is missing, but a valid configurable option. However, as @dfunckt says:

You can’t really add a new required property for example, because that would prevent eg the CLI from configuring an older OS nor make a required one optional, because the OS would bork without its presence — we have this issue for the “mixpanelToken” attribute now

This is because the different versions of the OS potentially 'require' different config options. Hence, we also need to version it.