Context:
The Writer for external events currently uses upsert requests along with generating a dynamic document id on demand. As the id is anyway dynamic we could simplify this to a simple index request though, during event processing anyway the user defined event.id is used for correlation thus only the latest event with a particular id wins.

Additionally we could also evaluate removing the custom id generation as its never referred and would speed up the index performance according to https://www.elastic.co/guide/en/elasticsearch/reference/master/tune-for-indexing-speed.html#_use_auto_generated_ids

AT:

• external event writer uses index requests rather than upsert
• remove dynamic doc id assignment and let elastic generate the id's