Pass Elastic errors as events, instead of logging them

[mfelsche]

Describe the problem you are trying to solve

In order to properly react to errors coming from requests sent via elastic sink, the overall errors and the bulk-element errors should be sent as error events to the err port of the sink. Currently bulk element errors are only logged at the ERROR level, which might quickly fill up disks. Also with error events with a proper format, users are going to be able to handle failures according to their business logic (retry policies while maintaining idempotency etc. etc.)

Describe the solution you'd like

Send all sink errors as Error events. This includes bulk element errors. These might be sent as separate events or as part of a single event which contains an array of all bulk errors.

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[mfelsche]

We want to extend this change to make the elastic sink a "Linked Transport" in that it will emit success and error events for each bulk item coming back.