Read 'event_id' of tracked events for third party integration

Unfortunately I can’t think of an reasonable alternative in V2.

Upgrading to V3 might not be a huge effort, I think that’d be worth investigating. There are two main breaking changes to watch out for, which are documented here: Migrating from v2 to v3 - Snowplow Docs

V3 release info: Introducing Version 3.0 of the Snowplow JavaScript Trackers (Browser and Node.js)