New API query parameter that automatically includes dependent metrics in report output

[diosmosis]

Summary

Refs matomo-org/looker-studio-connector#3
Refs matomo-org/looker-studio-connector#29
Refs #21937

In the Looker Studio connector, in order to support further grouping of processed metrics, the connector will need to be able to automatically query the metrics that processed metrics depend on.

For example, when querying for bounce_rate, the bounce_count and nb_visits need to be returned as well. With the metadata in #21937, we'll be able to tell Looker Studio how to compute bounce_rate, so the data to do that computation, must exist in the API response.

This is not the default behavior in Matomo. Normally, when a metric like bounce_rate is queried, the metrics needed to compute it will be queried from the database, but will be discarded after the computation is done. For Looker Studio, the connector needs a way to keep the discarded metrics.

A new query parameter in the Reporting API (eg, include_temporary_metrics=1) that provides this behavior is a possible solution.

[diosmosis]

This appears to already exist as showRawMetrics=1 (see DataTablePostProcessor::applyRequestedColumnDeletion()).