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.

プラグインの現在のフィールドとペイロードの構造から始め、リンクされている Grafana の correlations ドキュメントと、issue に記載されている Inspector の出力を使用します。生成されたログフィールドを、correlations が想定する安定した Line フィールドと比較します。Google Cloud Logging の結果から、ログ、メトリクス、またはトレースに使用できる相関ソースが取得できれば完了です。

索引モデルが issue の本文から書いたものです。