Clarify scenarios for the backup and restore guide

Current state
The backup and restore guide doesn't mention all of the prerequisites for the procedure. i.e. how can a customer know if this should be performed on the same cluster or a separate cluster?

Desired state
The current backup and restore guide describes the steps for restoring 3scale in another cluster, it assumes that the existing OCP cluster has become unavailable.  It should be clear about this. 

Also It would be helpful to describe the scenario when the backup and restore happens in the same cluster because there should be no 3scale artifacts left over from the previous deployment, otherwise there would be some collisions, for example the routes.