Adding `event.received` to APM events

Recently we added support for `event.received` field in apm-data: https://github.com/elastic/apm-data/pull/85

As part of data ingestion one interesting element we want to keep track of is when a certain event has been received by the ingestion backend.

This timestamp is not user-controlled like `@timestamp` and can guarantee us a certain timestamp for event reception, the step before ingestion (which is registered as event.ingested).

We also added setting the value for this field to OTLP ingested events, but we are lacking the same for APM events.

We also need to update APM server integration package data streams to provide proper mapping for the new field.