Make Content Pack Installation Aware of Existing Entities

[kingzacko1]

What?

Right now for all entity types, with the exception of Streams, if you export an entity into a content pack and then install it on a new system all dependent entities will be recreated even if they already exist on the server. This creates clutter and potential confusion about which entities are which since they are given identical names.

Previously, we added the Stream Reference content pack entity that exports a Stream Title and attempts to match it with an existing stream on the server before creating a new stream entirely. This allowed for Illuminate content to be shipped that referenced streams without recreating the streams each time the content was installed. A similar approach could work for all content pack exportable entities.

Why?

To keep Graylog servers clean of duplicate entities and make the process of installing content packs cleaner.

Relevant Issues/Feature Requests that ask for some piece of this FR or would be handled by its implementation:
#19065
#15736
#15107
#14672
#3517