Ctrl-c no longer stops server if plugin is running

[pauldix]

Found when running the example system metrics schedule plugin. After it's started, ctrl-c no longer stops the InfluxDB process. This will start the example (assuming you've created the mydb database):

./influxdb3 create trigger --trigger-spec "every:5s" --plugin-filename "gh:examples/schedule/system_metrics/system_metrics.py" --database mydb system-metrics