vapour_vrt() needs an overview picker

[mdsumner]

set a level, a resolution, or a dimension

Use this:

url <- "https://services.ga.gov.au/gis/rest/services/Topographic_Base_Map/MapServer/WMTS/1.0.0/WMTSCapabilities.xml,layer=Topographic_Base_Map,tilematrixset=default028mm"
dsn <- sprintf("WMTS:%s,layer=Topographic_Base_Map,tilematrixset=default028mm", url)
info <- vapour::vapour_raster_info(dsn)
## level 13 is a reasonable size to experiment with
(overviews <- matrix(info$overviews, ncol = 2, byrow = TRUE))

dm <- overviews[13L, , drop = TRUE]

which I'm using in grout.

[mdsumner]

done in de37ebf