Feature Request: Ability to correlate logs with other data sources

The recently announced [correlation](https://grafana.com/docs/grafana/latest/administration/correlations/) feature in Grafana enables data correlation between any enabled data sources.

We want to be able to correlate logs from Google Cloud Logging plugin with other observability data (not in GCP) like metrics and traces.

In practice this means adding Links to a Log Panel in Grafana Explore that use correlation variables:

In this example I used a Loki data source with some dummy data to configure log correlation with traces and metrics.
One thing that's required for a correlation is to know what field the log line is in. This can be checked in Grafana Explore by clicking the Inspector and then viewing the Data tab:

In this case the required field is Line which is used as an input for configuring source data in the correlation configuration page:

When I use the Inspector for logs in Google Cloud Logging plugin I get a different field for each log entry (see the csv examples attached), which makes it impossible to define correlations for our logs.

I also tried using regex to extract `resoure.labels.pod_name` from the content field, but unfortunately it doesn't seem to work. The regex I used: `resource.labels.pod_name="(.+?)"`

I suspect that Grafana treats (content + payload) as a field name and a log entry as the field value. So any regex would be checked against the field value, which is why it's not possible to make it work with the current field + payload structure.

It would be great if the plugin could work with the new correlation feature as it enables us to improve our troubleshooting experience.

Beginne mit der aktuellen Feld- und Payload-Struktur des Plugins und verwende dabei die verlinkte Grafana-correlations-Dokumentation sowie die in diesem Issue beschriebene Inspector-Ausgabe. Vergleiche die generierten Log-Felder mit dem stabilen Line-Feld, das von correlations erwartet wird; abgeschlossen ist die Aufgabe, wenn die Ergebnisse von Google Cloud Logging eine nutzbare Korrelationsquelle für Logs, Metriken oder Traces bereitstellen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.