Conform to GDAL Warp -ovr Overview Selection Options

[moradology]

The OverviewStrategy trait and subclasses (https://github.com/locationtech/geotrellis/blob/master/raster/src/main/scala/geotrellis/raster/io/geotiff/OverviewStrategy.scala) exist to capture the gdal warp command line -ovr options (https://gdal.org/programs/gdalwarp.html#cmdoption-gdalwarp-ovr)

We currently represent Auto-N and None (Base as we've named things) but do not represent explicit overview level selection or for that matter, the default GDAL behavior of Auto (AutoHigher behaves slightly differently). The OverviewStrategy types should work as they are described in GDAL docs