DS-2069 Edit item via swordv2 using its handle

https://jira.duraspace.org/browse/DS-2069

Currently, to update a DSpace item using Swordv2, one needs to know the item's internal ID. 

Example of replace: PUT /swordv2/edit-media/INTERNAL-ID 

But it would be of extreme importance if one could use the handle as well to do the update. Something like: 

PUT /swordv2/edit-media/ITEM-HANDLE 

Which would be similar to Swordv1 deposit: 

POST /sword/deposit/COLLECTION-HANDLE 

This need popped out because I needed to sync (add and update if it was previously added) a system with DSpace using Swordv2 and only knowing the item's handle. That's way I think this is an interesting/valuable feature to be added to DSpace. 
As soon as possible a pull-request will be made.