There should be an option to clean up after the successful completion of a migration plan.  If enabled, the plan and all associated VMs and their storage should be garbage collected.

• As a VM owner I would like all stale resources left over after a successful cross-cluster live migration to be cleaned up by the system so that I don't have to go back and manually delete things which could be confusing and error prone.

Notes:

• We should decide if deletion is immediate or delayed
• Should other migrated resources (such as ConfigMaps and Secrets) also be deleted?  How can we be certain that they are no longer needed on the source cluster?
• We may want to wait until we move the logic out of MTV and into CNV before adding this capability because it may be disruptive to MTVs concept of migration plans.