feat(automations): add event trigger source, selector and registration

surfsense_backend/app/automations/triggers/builtin/event/definition.py

@@ -0,0 +1,16 @@
+"""``event`` ``TriggerDefinition`` registration."""
+
+from __future__ import annotations
+
+from app.automations.triggers.store import register_trigger
+from app.automations.triggers.types import TriggerDefinition
+
+from .params import EventTriggerParams
+
+EVENT_TRIGGER = TriggerDefinition(
+    type="event",
+    description="Fire when a matching domain event is published.",
+    params_model=EventTriggerParams,
+)
+
+register_trigger(EVENT_TRIGGER)