* docs(influxdb3): document trigger logging behavior
Add processing_engine_logs table documentation to system data reference,
explaining that logs are stored in both the trigger's database (primary)
and _internal. Update plugins error handling to specify trigger's database.
* Update content/shared/influxdb3-plugins/_index.md
- Revises Paul's draft for using /api/v3/query_sql to query system data.
- Copies the existing structure for Ded. and Clustered
- Adds an explicit POST example for a longer query.