Add "subscribe" option to alert when new clients are moved or created

[MaryHirsch]

Clarivate use case:

New allocators/providers are created (specifically ones that used to be part of Purdue and CDL)

New functionality:
Option to “subscribe” in order to get notifications when a new allocator/provider is created or the movements of existing Datacenters?

Being notified of such changes would be highly beneficial.

Front conversations

[mfenner]

We provide similar functionality already. You can get a list of all clients sorted by creation date via the API: https://api.datacite.org/clients?sort=-created. This can be processed in regular intervals to detect new clients.