OptionalfetchDefaults to the global fetch.
OptionalheadersMerged over the NDJSON content-type (so it can be overridden), e.g.
{ authorization: 'Splunk <token>' }.
OptionaltransformPer-event reshaping for SIEM-specific envelopes — Splunk HEC wants
(event) => ({ event }). Default: the event itself.
HTTP event-collector URL (Splunk HEC, Datadog intake, Elastic, ...).