Context:

See PR conversation: https://github.com/camunda/camunda-optimize/pull/3817#discussion_r694027184 

The ingestionTimestamp of ingested events is set twice, once in the restService and then again once in the writer. Currently it's not clear why, presumably this was a mistake. Lets double check that this was indeed added accidentally and if so, remove the duplication and only set it once.

AT:

• event ingestion timestamp is only set once