The backup restore procedure should describe how to restore in an existing installation

Currently the restore portion of the backup restore procedure assumes the data will be restored in a new environment without 3scale installed.

This is not always desired. Often it will be required to restore an existing installation. The documentation should describe how to handle this in the first section which says to restore the secrets and run the new-app command. These commands will fail in an existing environment as they already exist.

There should also be a recommendation to scale down all pods while the restoration is in process to avoid any components attempting to write to the database while it is being restored. Which would then imply that we need a section about scaling them back up in the appropriate order at the end.