Upgrade to new COG support

[jswk]

As mentioned in #9, try using the new COG support, which may bring some artifacts/performance improvements. Also, it will most likely be far more stable than s3-geotiff.

As the official COG support was added, s3-geotiff is being deprecated, and will most likely be removed in future versions.
There is a thread about this at geotools-devel: https://sourceforge.net/p/geotools/mailman/message/37293270/ (see if there weren't updates since 20210531 as it's fresh). And a bug, where people have problem with older version of ehCache: https://osgeo-org.atlassian.net/browse/GEOS-9866 used by it.