Remove rebalance watcher once CB server supports new-line output

MB-46480 provides an update to rebalance report output to remove the need to pre-process the reports just to add a newline.

Once this is available in a server version, we need to provide a mechanism to enable/disable based on server version (whilst we're still supporting versions using the old format). Likely just a config change in operator by default using the server image version.

This also removes all the complexity of managing the temporary copies so eventually we should remove it all from the implementation.