Grafana could reach the swarm's metrics and not its logs, so the store that
landed with the collector pipeline had no reader.
Adds the VictoriaLogs datasource plugin and the Logs Drilldown app, and
provisions the datasource beside the metrics one. The drilldown matters as much
as the connection: an unfamiliar log stream is explorable without writing a
LogsQL query first, which is the difference between a store you can query and
one you can use.
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