Grafana 13 externalised its core data sources; nixpkgs no longer bundles
the Elasticsearch datasource, so every DMARC panel failed with "Plugin not
registered". Load the official Grafana-signed elasticsearch plugin via
declarativePlugins, pin the dmarc-ag/dmarc-fo datasource UIDs (Grafana 11+
resolves datasource template variables by UID, not name), and clear stale
uid-less records left by an earlier deploy.
Berwn
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