Allow user to select a feature for display in Reports

[qgib]

Author Name: Spencer Gardner (@spencerrecneps)
Original Redmine Issue: 20954

Redmine category:map_composer/printing

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When building a report it is useful to populate the layouts using information from actual features in the dataset. A user can cause the Report to populate with a feature's information by exporting the whole layout (presumably because this activates the Atlas in the background). It would be nice to be able to toggle this without having to export the report. In addition, it would be helpful to allow users to select the feature used for display so they can check multiple features in the layout.

This functionality is already made available in regular Atlas layouts with a dropdown. I would think the easiest solution would be to implement the same thing in Reports.