**Related to:** https://github.com/elastic/kibana/pull/94143
## Summary
This PR adds new fields to the schema (`EventSchema`, `IEvent`):
- standard ECS fields: `error.*`, `event.*`, `log.level`, `log.logger`, `rule.*`
- custom field set `kibana.detection_engine`
We need these fields on the Detections side to implement detection rule execution log. See the related proposal (https://github.com/elastic/kibana/pull/94143) for more details.
Also, this PR bumps ECS used in Event Log from `1.6.0` to the current `1.8.0` version. They are 100% same in terms of fields used in Event Log, so no changes in the schema were caused by this version increment.