Add "ManagedBy" field to ZFS datasets and Shares

Recording this ticket for further discussion. We'd like to see about an optional field getting added to the API when we create any new dataset/share which can be used to mark if the said item was created by a 3rd party system. I.E. TrueCommand or vCenter.

When displaying or attemping to edit/destroy these items in the regular UI, we'd like a prompt to warn the user that this item was created by <external service>, are you sure you want to change it?

This is to help prevent foot-shooting when some 3rd party service potentially is creating new datasets/shares and might get cranky if something is changed / destroyed outside of its management interfaces.