* Pass the actual date args that are returned in fixtures (just for clarity)

* Change select key from operating_system to os

* Select (not set) from imported data as done from native stats

* Support breakdown by imported os_version

* Remove dead code

The `query.include_imported` is set to `false` from the start when
filters are included.

* Refactor Plausible.Stats.Imported

Extract a function that does group_by and dimension select, instead of
doing both separately inside the merge_imported function body

* Further refactor of Plausible.Stats.Imported

Get rid of code repetition

* Support breakdown by imported browser_version

* Support breakdown by imported referrer

* Support breakdown by imported referrer

* remove redundant if in select

* use greatest instead of coalesce

Co-authored-by: ruslandoga <doga.ruslan@gmail.com>

* add back the :member filter handling in Stats.Imported

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Co-authored-by: Uku Taht <uku.taht@gmail.com>
Co-authored-by: ruslandoga <doga.ruslan@gmail.com>