Investigate algorithm for establishing a tile sets minimum zoom

[stevendlander]

When a raster image is tiled, SWAGD first checks to see what zoom levels the image would be valid for. Our goal is to start at a zoom level that has only one tile (min zoom or lowest integer zoom).

This is determined in GdalUtility.zoomLevelForPixelSize(). Adjust this algorithm so we don't have to check in GdalUtility.getMinimalZoom to see if we need to reduce the min zoom any further.

[stevendlander]

A minimal zoom for a raster image should be the zoom level on which the raster image would produce a map area roughly equivalent to a tile (256, 512, etc). See line 1176 of gdal2tiles_parallel in geopackage-python repo.

The python functionality should be mimic'd as much as possible.