Attach dashcard's viz settings to the card's :data :viz-settings key (#36067)

* Attach dashcard's viz settings to the card's :data :viz-settings key

This flows through to the export format fn `metabase.email.messages/stream-api-results-to-export-format`
Where it is then properly used.

* Added test that gets the contents of .csv attachments

Not sure yet why it's not working. Locally, with a real db id it works as expected, so it's on the right track.

* Create a working test.

* Card qp merges dashcard viz when it exists. Viz middleware normalizes card/dashcard viz-settings

* Addressed feedback.

 - if viz settings map is empty in process viz settings middleware, use qp store.
 - now we don't have to do the (or ...) logic anywhere else
 - added comment in the test to try clarify what the 'viz' is setting up