Enable selection of heatmap orientation
Enable selection of heatmap orientation

Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/non-clustered-heatmaps-and-flipping.gmi

* Provide the user with the UI elements to enable them select the
  orientation of the heatmap that will be produced.

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