Support migrating to a different namespace on restore

[sseago]

Cloned fusor/ocp-velero-plugin#42 to the new repo

In conjunction with migtools/mig-controller#90 we'll need support in the plugin for changing namespace on restore. I believe that there is already some level of support at the velero level for this, but the restore plugins will need to be modified to support this. At the very least, the image copy code and the image reference swapping will need to be aware of the target/destination namespace change.

(might need change in the general plugin repo too)