Enable/Disable rendering of thumbnails on map on a per-collection or per-item basis

Some thumbnails show nicely on a map (usually S2), but especially for larger extents or complex geometries this doesn't work anymore and leads to smeared thumbnails. There should be a way to enable/disable this on a per-collection basis, e.g. through collection-level configuration via JSON or an option in STAC Browser. Or a specific role, e.g. `example`.