Add device deletion and creation triggers #1016
Description
Astarte 1.2 introduced device deletion. Since deletion is asynchronous, a "device deleted" trigger could be a straightforward way to provide a user with information on the end of the operation.
Dually, a "device created" trigger might be introduced.
Note that the related operations are carried out by Realm Management and Pairing respectively, so it could be possible that these triggers are not generated by Data Updater Plant, differently from all others. This topic must be further investigated.