It’s not in the docs because it’s more of a building block than something that end users would normally be using. But there is a GenericEventTrigger.
But be aware that this can be triggered on any and all OH events: thing status changes, channel events, rules running or going to idle, Items being created, loaded, system runlevels, etc. Bring up the developer sidebar and open the event stream. Everything you see there can be used to trigger a rule.
To use this trigger successfully, you’ll need to have an intimate knowledge of the event bus, event topic structure, and different data that is available for each type of event. See Event Bus | openHAB.
For an example of it’s use, in the UI but you should be able to translate it to a JSRule trigger using the links from above, see Thing Status Reporting [4.0.0.0;4.9.9.9] which filters on the ThingStatusChanged events.