[Request] Optional footprint polygons in volume map

[BNAndras]

Describe the feature or enhancement you're looking for
Volume map viewer should optionally show the footprint/extent of layers rather the layer itself.

If this request is linked to a problem, please describe.
Primarily, this would be useful in identifying bad extents like https://oldinsurancemaps.net/layers/geonode:bastrop_la_1907_p1_1. It could also be helpful for viewing the area covered by the maps without fiddling with transparency.

Describe alternatives you've considered
Bad extents could also be identified by reviewing individual item thumbnails.

[mradamcox]

Though the "bad extent" issue this ticket refers to is no longer a problem with the updated architecture, a request just came in very similar to this to add display of page numbers on the layers in the volume preview. Perhaps a "data" toggle could be added here, that would add the extents as described above, as well as the text labels in the centroid of each layer.