Allow namespace admins to clone snapshots created by them

Creating a snapshot requires table admin permissions. But cloning it requires global admin permissions unless the user owns the snapshot and wants to recreate the original table the snapshot was based on using the same table name. This puts unnecessary load on the few people having global admin permissions. I would like to relax this rule a bit and allow the owner of the snapshot to clone it into any namespace where they have admin permissions regardless of the table name used.