alterationType entityDelete support for Transient Entities

[fgalan]

Is your feature request related to a problem / use case? Please describe.

At the present moment, Transient Entities (https://github.com/telefonicaid/fiware-orion/blob/master/doc/manuals/orion-api.md#transient-entities) are silently deleted by MongoDB, so Orion doesn't get aware of the removal so it cannot notify based on it when entityDelete alterationType (https://github.com/telefonicaid/fiware-orion/blob/master/doc/manuals/orion-api.md#subscriptions-based-in-alteration-type) is used.

Describe the solution you'd like

Support entityDelete alterationType with Transient Entities.

Describe alternatives you've considered

Maybe this can be useful: https://www.mongodb.com/docs/manual/changeStreams/

Describe why you need this feature

• To improve or simplify an scenario.

Additional information

Nothing to say.

[tzzed]

Something like a table as journal that contains transient entities with a daily check of the deletion.