Allow better drilldown of data

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In the default view, the Campaign Name is hierarchical, with a subtable available for "Keyword - Content".
Since campaigns very often are run across different channels/sources, I feel that a more relevant subtable would instead be "Source - Medium" instead of "Keyword - Content". Could this perhaps be added as an option somewhere in order for the user to personalize?

Additionally - and I'm not sure how computationally expensive this would be - but ideally, I would love the possibility to drill down in the data, in the following sequence (i.e. with a subtable for each new subtable):

```
Campaign Name
---
Campaign Source - Medium
--
Campaign Content
--
Entry Page URL
```

I'm no Matomo expert - and maybe the above could be achieved with a custom report? - but perhaps the above suggestion would be something useful also to other non-powerusers.

Start with the default Campaign Name report and trace how its existing Keyword - Content subtable is defined. Compare that behavior with the requested Source - Medium option and the proposed nested sequence through Campaign Content and Entry Page URL. Done would require a decided personalization or custom-report approach and verified drilldown behavior.

Written by the indexing model from the issue text.