upgrade-manager-v2: Delete old rollups upon upgrade-manager start.

[shreyas-badiger]

Everytime upgrade-manager starts, it must delete all the previous rollups.

[shrinandj]

Deleting all rolling-upgrades upon controller restarts could be dangerous. This should be done at least via a config option. If a particular rolling-upgrade object is causing the controller to crash and restart, there is value is keeping the rolling-upgrade object around for debugging purposes.

Another option (and maybe inline with other Kubernetes objects) is to have a ttlAfterCompletion value in each rolling-upgrade object. The controller should run a GC task periodically and clean up all rolling-upgrade objects if their ttlAfterCompletion has passed.