Aggregation in Ingest Pipeline of Elastic Agent - Custom Logs integration

Currently I have a Logstash pipeline parsing, aggregating and finally delivering Postfix logs to the Elasticsearch. I want to retire Logstash completely and use Fleet to deploy a policy with Custom Logs integration. I managed to parse the logs but I'm not at the last step at which I need to aggregate them based on a field.
(Postfix logs are structured in a way such as one logical process of a mail is split into numerous "physical" processes and thus loglines, only ever to be connected by the "queueid", which is a successfully parsed field by this time)

Basically I need to equivalent in Elastic Ingest Pipeline Processor of the following Logstash snippet:

filter {
  if ![queueid] {
    drop {}
  } else {
    aggregate {
      task_id => "%{queueid}"
      aggregate_maps_path => "/inputs/.aggregate_maps"
      code => "
      map_action => "create_or_update"
      push_previous_map_as_event => false
      push_map_as_event_on_timeout => true
      timeout => 30
      timeout_tags => ['aggregated']

How would one be able to reproduce such functionality in terms of Ingest Pipeline's processors?