[Filebeat] Specify Elasticsearch Ingest Pipeline with Hints-Based Autodiscover

How can I specify a custom Elasticsearch Ingest Pipeline for use with hints-based autodiscover. E.g., I would like to be able to include it as a pod annotation, rather than hardcode it into the autodiscover specification.

It appears that this is available as of filebeat-8.1.x. I'm still using 7.15.0, and so will need to upgrade.